| 2021 Ostrava Challenger | |
|---|---|
| Date | 26 April – 2 May |
| Edition | 18th |
| Surface | Clay |
| Location | Ostrava, Czech Republic |
| Champions | |
| Singles | |
 Benjamin Bonzi | |
| Doubles | |
 Marc Polmans /  Sergiy Stakhovsky | |
The 2021 Ostra Group Open was a professional tennis tournament played on clay courts. It was the 18th edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Ostrava, Czech Republic between 26 April and 2 May.
| Country | Player | Rank1 | Seed |
|---|---|---|---|
| FRA | Grégoire Barrère | 118 | 1 |
 BRA | Thiago Seyboth Wild | 124 | 2 |
| FRA | Benjamin Bonzi | 127 | 3 |
| FRA | Arthur Rinderknech | 129 | 4 |
| AUS | Marc Polmans | 148 | 5 |
 USA | Maxime Cressy | 156 | 6 |
 CHI | Alejandro Tabilo | 162 | 7 |
 EGY | Mohamed Safwat | 164 | 8 |
The following players received wildcards into the singles main draw:
Martin Krumich Jiří Lehečka Patrik Rikl The following player received entry into the singles main draw as an alternate:
The following players received entry from the qualifying draw:
Benjamin Bonzi def. 
Renzo Olivo 6–4, 6–4. Marc Polmans / Sergiy Stakhovsky def. Andrew Paulson / Patrik Rikl 7–6(7–4), 3–6, [10–7].
