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            <identifier scheme="http://www.sec.gov/CIK">0001383414</identifier>
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    <dei:EntityRegistrantName contextRef="P01_30_2026To01_30_2026" id="ixv-316">PennantPark Investment Corporation</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode contextRef="P01_30_2026To01_30_2026" id="ixv-317">MD</dei:EntityIncorporationStateCountryCode>
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    <dei:EntityTaxIdentificationNumber contextRef="P01_30_2026To01_30_2026" id="ixv-319">20-8250744</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1 contextRef="P01_30_2026To01_30_2026" id="ixv-320">1691 Michigan Avenue</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown contextRef="P01_30_2026To01_30_2026" id="ixv-321">Miami Beach</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince contextRef="P01_30_2026To01_30_2026" id="ixv-322">FL</dei:EntityAddressStateOrProvince>
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    <dei:Security12bTitle contextRef="P01_30_2026To01_30_2026" id="ixv-330">Common Stock, par value $0.001 per share</dei:Security12bTitle>
    <dei:TradingSymbol contextRef="P01_30_2026To01_30_2026" id="ixv-331">PNNT</dei:TradingSymbol>
    <dei:SecurityExchangeName contextRef="P01_30_2026To01_30_2026" id="ixv-332">NYSE</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany contextRef="P01_30_2026To01_30_2026" id="ixv-333">true</dei:EntityEmergingGrowthCompany>
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    <cef:LongTermDebtStructuringTextBlock contextRef="P01_30_2026To01_30_2026" id="ixv-172">&lt;div style="margin-top:6pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;On January&#160;30, 2026, PennantPark Investment Corporation (the &#x201c;Company&#x201d;) entered into a Note Purchase Agreement (the &#x201c;Note Purchase Agreement&#x201d;) governing the issuance of $75,000,000 in aggregate principal amount of 7.00% Senior Unsecured Notes due February&#160;1, 2029 (the &#x201c;Notes&#x201d;), to a qualified institutional investor (the &#x201c;Investor&#x201d;) in a private placement (the &#x201c;Private Placement&#x201d;). &lt;/div&gt; &lt;div style="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;Interest on the Notes will be due semi-annually on the 1st day of February and August each year, beginning on August&#160;1, 2026. The Notes may be redeemed in whole or in part at any time or from time to time at the Company&#x2019;s option at par plus accrued and unpaid interest to the pr&lt;div style="display:inline;"&gt;epaym&lt;/div&gt;ent date and, if prior to November&#160;1, 2028, a make-whole premium. In addition, the Company is obligated to offer to prepay the Notes at par plus accrued and unpaid interest up to, but excluding, the date of prepayment, if certain change in control events occur. The Notes are general unsecured obligations of the Company that rank &lt;div style="font-style: normal; letter-spacing: 0px; top: 0px;display:inline;"&gt;&lt;div style="font-style:italic;display:inline;"&gt;pari passu&lt;/div&gt;&lt;/div&gt; with all outstanding and future unsecured unsubordinated indebtedness issued by the Company. &lt;/div&gt;</cef:LongTermDebtStructuringTextBlock>
    <cef:LongTermDebtTableTextBlock contextRef="P01_30_2026To01_30_2026" id="ixv-173">&lt;div style="margin-top:6pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;On January&#160;30, 2026, PennantPark Investment Corporation (the &#x201c;Company&#x201d;) entered into a Note Purchase Agreement (the &#x201c;Note Purchase Agreement&#x201d;) governing the issuance of $75,000,000 in aggregate principal amount of 7.00% Senior Unsecured Notes due February&#160;1, 2029 (the &#x201c;Notes&#x201d;), to a qualified institutional investor (the &#x201c;Investor&#x201d;) in a private placement (the &#x201c;Private Placement&#x201d;). &lt;/div&gt;</cef:LongTermDebtTableTextBlock>
    <cef:LongTermDebtPrincipal
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      id="ixv-335"
      unitRef="Unit_USD">75000000</cef:LongTermDebtPrincipal>
    <cef:LongTermDebtDividendsAndCovenantsTextBlock contextRef="P01_30_2026To01_30_2026" id="ixv-179">&lt;div style="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;The Note Purchase Agreement contains customary terms and conditions for senior unsecured notes issued in a private placement, including, without limitation, affirmative and negative covenants such as information reporting, and a minimum asset coverage ratio of 1.50 to 1.00. &lt;/div&gt;&lt;div style="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;The Note Purchase Agreement also contains customary events of default with customary cure and notice periods, including, without limitation, nonpayment, incorrect representation in any material respect, breach of covenant, certain judgments and orders and certain events of bankruptcy. &lt;/div&gt;&lt;div style="margin-top:12pt; margin-bottom:0pt; font-size:10pt; font-family:Times New Roman"&gt;In connection with the Private Placement, the Company entered into a Registration Rights Agreement, dated as of January&#160;30, 2026 (the &#x201c;Registration Rights Agreement&#x201d;), with the Investor. Pursuant to the Registration Rights Agreement, the Company is obligated to file with the Securities and Exchange Commission a registration statement with respect to an offer to exchange the Notes for a new issue of debt securities registered under the Securities Act of 1933, as amended (the &#x201c;Securities Act&#x201d;), with terms substantially identical to those of the Notes (except for provisions relating to transfer restrictions and payment of additional interest) and to use its commercially reasonable efforts to consummate such exchange offer on the earliest practicable date after the registration statement has been declared effective but in no event later than 365 days after the initial issuance of the Notes. If the Company is not able to effect the exchange offer, the Company will be obligated to file a registration statement covering the resale of the Notes and use its commercially reasonable efforts to cause such registration statement to be declared effective. If the Company fails to satisfy its registration obligations by certain dates specified in the Registration Rights Agreement, the Company will be required to pay additional interest to the holder of the Notes. &lt;/div&gt;</cef:LongTermDebtDividendsAndCovenantsTextBlock>
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