The 2021 Belgrade Challenger was a professional tennis tournament played on clay courts. It was the ninth edition of the tournament which was part of the 2021 ATP Challenger Tour.[1] It took place in Belgrade, Serbia between 12 and 18 April 2021.
For the first time, a women's tournament was also held between 26 and 31 July, categorized as a WTA 125[2] event at the same venue, which was part of 2021 WTA 125K series.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Spain | Roberto Carballés Baena | 98 | 1 | |
 Argentina | Facundo Bagnis | 104 | 2 | |
 Colombia | Daniel Elahi Galán | 110 | 3 | |
| Philipp Kohlschreiber | 112 | 4 | ||
| Argentina | Francisco Cerúndolo | 114 | 5 | |
 Japan | Taro Daniel | 117 | 6 | |
 Bolivia, Plurination;al State of | Hugo Dellien | 121 | 7 | |
 France | Benjamin Bonzi | 125 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry into the singles main draw as special exempts:
The following players received entry from the qualifying draw:
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Russian Federation | Anna Blinkova | 83 | 1 | |
| Arantxa Rus | 85 | 2 | ||
| Russian Federation | Varvara Gracheva | 89 | 3 | |
| Andrea Petkovic | 97 | 4 | ||
 Italy | Martina Trevisan | 102 | 5 | |
| Kaja Juvan | 107 | 6 | ||
 Romania | Irina Bara | 116 | 7 | |
| Viktoriya Tomova | 117 | 8 |
The following players received wildcards into the singles main draw:
Iva Šepa Draginja VukovićThe following players received entry from the qualifying draw:
Ana Bogdan → replaced by Tereza Mrdeža Elisabetta Cocciaretto → replaced by 
Lesia Tsurenko
Zarina Diyas → replaced by 
Olga Govortsova Océane Dodin → replaced by Amandine Hesse Sara Errani → replaced by Jaqueline Cristian
Rebecca Šramková Anna Kalinskaya → replaced by Andrea Petkovic Jasmine Paolini → replaced by Jana Fett Elena-Gabriela Ruse → replaced by 
Panna Udvardy Aliaksandra Sasnovich → replaced by Isabella Shinikova Patricia Maria Țig → replaced by Susan Bandecchi Olga Danilović| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| Russian Federation | Natela Dzalamidze |  Georgia | Oksana Kalashnikova | 251 | 1 | |
| Belarus | Olga Govortsova | Belarus | Lidziya Marozava | 355 | 2 | |
 Norway | Ulrikke Eikeri | Hungary | Panna Udvardy | 378 | 3 | |
| France | Estelle Cascino | Italy | Camilla Rosatello | 382 | 4 |
The following pair received a wildcard into the doubles main draw:
See main article: 2021 Belgrade Challenger – Men's singles.
Roberto Carballés Baena def. 
Damir Džumhur 6–4, 7–5.See main article: 2021 Belgrade Challenger – Women's singles.
Anna Karolína Schmiedlová def. Arantxa Rus 6–3, 6–3See main article: 2021 Belgrade Challenger – Men's doubles.
Guillermo Durán / Andrés Molteni def. Tomislav Brkić / Nikola Ćaćić 6–4, 6–4.See main article: 2021 Belgrade Challenger – Women's doubles.
Olga Govortsova / Lidziya Marozava def. Alena Fomina / Ekaterina Yashina 6–2, 6–2