| Doubles | |
|---|---|
| 2021 Open de Oeiras II | |
| Champions |  Nuno Borges Francisco Cabral |
| Runners-up |  Pavel Kotov  Tseng Chun-hsin |
| Score | 6–1, 6–2 |
This was the second of four editions of the tournament in the 2021 ATP Challenger Tour calendar. [1]
Mats Moraing and Oscar Otte were the defending champions but withdrew from the tournament before their first round match.
Nuno Borges and Francisco Cabral won the title after defeating Pavel Kotov and Tseng Chun-hsin 6–1, 6–2 in the final.
Enzo Couacaud / Manuel Guinard (quarterfinals)
Harry Bourchier / 
Sergio Galdós (quarterfinals)
Hunter Johnson / Yates Johnson (first round) Gonçalo Falcão / 
Denis Yevseyev (first round)| First round | Quarterfinals | Semifinals | Final | ||||||||||||||||||||||||
| 1 | E Couacaud M Guinard | 6 | 6 | ||||||||||||||||||||||||
 D-h Lee G Oliveira | 0 | 2 | 1 | E Couacaud M Guinard | 3 | 7 | [6] | ||||||||||||||||||||
N Chappell  V Orlov | w/o | N Chappell V Orlov | 6 | 5 | [10] | ||||||||||||||||||||||
 M Moraing O Otte | N Chappell V Orlov | 2 | 1 | ||||||||||||||||||||||||
| 4 | Gonçalo Falcão D Yevseyev | 6 | 4 | [9] | N Borges F Cabral | 6 | 6 | ||||||||||||||||||||
| M Rosenkranz Tom Schönenberg | 3 | 6 | [11] | M Rosenkranz T Schönenberg | 65 | 1 | |||||||||||||||||||||
| N Borges F Cabral | 6 | 6 | N Borges F Cabral | 77 | 6 | ||||||||||||||||||||||
| WC | Eduardo Morais Vasco Prata | 1 | 3 | N Borges F Cabral | 6 | 6 | |||||||||||||||||||||
| WC | Miguel Gomes H Rocha | 1 | 2 | P Kotov C-h Tseng | 1 | 2 | |||||||||||||||||||||
E Escobedo  L Miedler | 6 | 6 | E Escobedo L Miedler | w/o | |||||||||||||||||||||||
 R Brancaccio  Eduard Esteve Lobato | 2 | 6 | [10] | R Brancaccio E Esteve Lobato | |||||||||||||||||||||||
| 3 | H Johnson Y Johnson | 6 | 2 | [5] | E Escobedo L Miedler | 6 | 2 | [6] | |||||||||||||||||||
| WC | J Faria Tiago Torres | 2 | 4 | P Kotov C-h Tseng | 4 | 6 | [10] | ||||||||||||||||||||
| P Kotov C-h Tseng | 6 | 6 | P Kotov C-h Tseng | 6 | 6 | ||||||||||||||||||||||
| GM Moroni R Ortega Olmedo | 2 | H Bourchier S Galdós | 4 | 4 | |||||||||||||||||||||||
| 2 | H Bourchier S Galdós | w/o | |||||||||||||||||||||||||
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