| Date: | 27 September – 3 October |
| Edition: | 6th |
| Category: | ATP World Tour 250 series |
| Prize Money: | €419,470 |
| Draw: | 28S / 16D |
| Surface: | Hard (indoor) |
| Location: | Sofia, Bulgaria |
| Venue: | Arena Armeec |
| Champs: |  Jannik Sinner[1] |
| Champd: |  Jonny O'Mara / Ken Skupski[2] |
| Main Name: | ATP Sofia Open Sofia Open |
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]
See main article: article and 2021 Sofia Open – Singles.
Jannik Sinner defeated 
Gaël Monfils 6–3, 6–4See main article: article and 2021 Sofia Open – Doubles.
Jonny O'Mara / Ken Skupski defeated 
Oliver Marach / Philipp Oswald, 6–3, 6–4| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Jannik Sinner | 14 | 1 | ||
| France | Gaël Monfils | 20 | 2 | |
 Australia | Alex de Minaur | 21 | 3 | |
 Kazakhstan | ||||
 Serbia | Filip Krajinović | 37 | 5 | |
| France | Adrian Mannarino | 43 | 6 | |
 Spain | 45 | 7 | ||
| Australia | John Millman | 48 | 8 |
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:
Roberto Bautista Agut → replaced by James Duckworth Alexander Bublik → replaced by 
Kamil Majchrzak Gianluca Mager
Mackenzie McDonald → replaced by 
Emil Ruusuvuori| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| Finland | Henri Kontinen |  Japan | Ben McLachlan | 81 | 1 | |
 Bosnia and Herzegovina | Tomislav Brkić | Serbia | Nikola Ćaćić | 93 | 2 | |
| Austria | Oliver Marach | Austria | Philipp Oswald | 95 | 3 | |
| Australia | Luke Saville | Australia | John-Patrick Smith | 97 | 4 |
The following pairs received wildcards into the doubles main draw:
The following pair received entry as alternates:
Jérémy Chardy / Hugo Nys → replaced by 
André Göransson / Hugo Nys Matthew Ebden / 
Jonathan Erlich → replaced by Jonathan Erlich / Dominic Inglot 
Sander Gillé / Joran Vliegen → replaced by Jonny O'Mara / Ken Skupski Marcos Giron / Mackenzie McDonald → replaced by Lorenzo Musetti / Andrea Vavassori Pedro Martínez / Jaume Munar → replaced by Plamen Milushev / Radoslav Shandarov
