Jaime Oncins (born 16 June 1970) is a former professional tennis player from Brazil.

Oncins represented his native country at the 1992 Summer Olympics in Barcelona, where he reached the quarterfinals before falling to Russia's Andrei Cherkasov.

Oncins' best performance at a major was at the 1992 French Open, where he reached the Round of 16, losing to eventual finalist, Petr Korda.

In the second round of the tournament, Oncins had a famous victory from two sets down against former world No.

Oncins was a runner-up in the Roland Garros mixed doubles in 2001, with Paola Suárez from Argentina.