The 2021 Open de Oeiras II was a professional tennis tournament played on clay courts.

It was the second edition of the tournament, part of the 2021 ATP Challenger Tour.

It took place in Oeiras, Portugal between 5 and 11 April 2021.

The following players received wildcards into the singles main draw: The following player received entry into the singles main draw as a special exempt: The following players received entry into the singles main draw as alternates: The following players received entry from the qualifying draw: