When performing aortic valve replacement in young patients, mechanical valves are recommended due to their durability. However, because mechanical valves require lifelong use of warfarin and carry risks such as easy bleeding, bioprosthetic valve replacement may be performed in some cases even in young patients. In this report, we describe a case of a patient who underwent bioprosthetic aortic valve replacement with aortic annular enlargement in anticipation of TAV in SAV and had a good postoperative course. The patient is a 51-year-old male. He was referred to our hospital for surgical treatment of severe aortic stenosis. The patient strongly preferred a bioprosthetic valve due to the disadvantage of taking warfarin. Therefore, we considered the possibility of TAV in SAV due to his young age, and decided to perform aortic annular enlargement if necessary. Intraoperatively, after resection and decalcification of the valve, a sizer was inserted, but the 19 mm sizer could not pass through, so we decided to perform aortic annular enlargement. Aortic annular enlargement was performed by suturing a Dacron patch and implantation of a 23 mm bioprosthetic valve. The patient had no major postoperative problems and was discharged home on the 14th day after surgery. In order to avoid PPM in the future when TAVI is performed, aortic annular enlargement should be considered in young patients undergoing aortic valve replacement using a bioprosthetic valve if TAV in SAV is considered to be difficult.