The 2021 Serbia Open was a tennis tournament played on outdoor clay courts. It was the 5th and 1st edition of the event for male and female professional tennis players, respectively. It was part of the 2021 ATP Tour and the 2021 WTA Tour and took place in Belgrade, Serbia; in mid-April for men and mid-May for women. A second ATP tournament, called the Belgrade Open, was played in men's singles the week before the French Open.
<sub>*per team</sub>
The following players received wildcards into the main draw:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
The following pairs received wildcards into the doubles main draw:
The following pair received entry as an alternate:
The following players received wildcards into the main draw:
The following players received entry using a protected ranking:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
The following pairs received wildcard<nowiki>s</nowiki> into the doubles main draw:
The following pair received entry into the doubles main draw using a protected ranking:
The following pair received entry as alternates: