2021 Belgrade Challenger

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. 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 event at the same venue, which was part of 2021 WTA 125K series.

ATP singles main-draw entrants

¹ Rankings are as of 5 April 2021.

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:

¹ Rankings are as of 19 July 2021.

The following players received wildcards into the singles main draw:

The following players received entry from the qualifying draw:

;Before the tournament

The following pair received a wildcard into the doubles main draw:

Roberto Carballés Baena def. Damir Džumhur 6–4, 7–5.

Anna Karolína Schmiedlová def. Arantxa Rus 6–3, 6–3

Guillermo Durán / Andrés Molteni def. Tomislav Brkić / Nikola Ćaćić 6–4, 6–4.

Olga Govortsova / Lidziya Marozava def. Alena Fomina / Ekaterina Yashina 6–2, 6–2