EXHIBIT 32.1(a)

CERTIFICATIONS 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 of Byline Bancorp, Inc. (the “Company”) on Form 10-Q for the period ended June 30, 2018 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, the Chief Executive Officer and Chief Financial Officer of the Company, each hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to his or her knowledge:

1.The Report fully complies with the requirements of Sections 13(a) or 15(d) of the Securities Exchange Act of 1934; and

2.The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/	Alberto J. Paracchini
	Alberto J. Paracchini
	President and Chief Executive Officer
	(Principal Executive Officer)
	August 10, 2018
/s/	Lindsay Corby
	Lindsay Corby
	Executive Vice President & Chief Financial Officer
	(Principal Financial Officer)
	August 10, 2018