| Date: | 6–12 September |
| Edition: | 19th |
| Surface: | Clay |
| Location: | Banja Luka, Bosnia and Herzegovina |
| Champs: |  Juan Manuel Cerúndolo |
| Champd: | Antonio Šančić / Nino Serdarušić |
| Before Year: | 2019 |
The 2021 Banja Luka Challenger was a professional tennis tournament played on clay courts. It was the nineteenth edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Banja Luka, Bosnia and Herzegovina from 6 to 12 September 2021.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Slovakia | Andrej Martin | 122 | 1 | |
| Argentina | Juan Manuel Cerúndolo | 135 | 2 | |
| Argentina | Tomás Martín Etcheverry | 142 | 3 | |
 Serbia | Nikola Milojević | 160 | 4 | |
 India | Sumit Nagal | 164 | 5 | |
| Serbia | Danilo Petrović | 177 | 6 | |
 Czech Republic | Zdeněk Kolář | 182 | 7 | |
| Czech Republic | Vít Kopřiva | 202 | 8 |
The following players received wildcards into the singles main draw:
Dražen Petrović Vladan Tadić Marko TopoThe following players received entry from the qualifying draw:
Jonathan Mridha David Poljak Marko TepavacSee main article: 2021 Banja Luka Challenger – Singles.
Juan Manuel Cerúndolo def. Nikola Milojević 6–3, 6–1.See main article: 2021 Banja Luka Challenger – Doubles.