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.

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: The following players received wildcards into the singles main draw: The following players received entry from the qualifying draw: The following pair received a wildcard into the doubles main draw: