Mariana Díaz Oliva (born 11 March 1976) is a former professional tennis player from Argentina. She played professionally from September 1992 until 12 October 2006. Her highest ranks were world No. 42 for singles and No. 93 for doubles, both achieved in 2001. At the 2001 Bol Open, she defeated Kim Clijsters to reach the final, where she lost to Ángeles Montolio. In 2002, she won the Internazionali Femminili di Palermo. In 2003, she also reached the Mexican Open singles final.

WTA Tour finals

Singles: 3 (1 title, 2 runner-ups)

Doubles: 2 (runner-ups)

ITF finals

Singles: 27 (16–11)

Doubles: 23 (15–8)