The 2021 Sofia Open was a men's tennis tournament played on indoor hard courts.

It was the sixth edition of the Sofia Open as part of the ATP World Tour 250 series of the 2021 ATP Tour.

It was played at the Arena Armeec in Sofia, Bulgaria, from 27 September to 3 October 2021.

First-seeded Jannik Sinner won the singles title.

[3] The following players received wildcards into the main draw: The following players received entry from the qualifying draw: The following player received entry as a lucky loser: The following pairs received wildcards into the doubles main draw: The following pair received entry as alternates: