Golub Capital BDC (GBDC) 10-Q2021 Q3 Quarterly report

Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of Golub Capital BDC, Inc. (the “Company”), for the quarterly period ended June 30, 2021, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), we, David B. Golub and Ross A. Teune, Chief Executive Officer and Chief Financial Officer, respectively, of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to our knowledge: