The 2004 Estoril Open was a tennis tournament played on outdoor clay courts at the Estoril Court Central in Oeiras in Portugal that was part of the International Series of the men's 2004 ATP Tour and of Tier IV of the women's 2004 WTA Tour.

It was the 15th edition of the tournament for the men (the 8th for the women) and was held from 12 April until 18 April 2004.

Juan Ignacio Chela and Émilie Loit won the singles titles.

Juan Ignacio Chela defeated Marat Safin 6–7(2–7), 6–3, 6–3 [1] Émilie Loit defeated Iveta Benešová 7–5, 7–6(7–1) [2] Juan Ignacio Chela / Gastón Gaudio defeated František Čermák / Leoš Friedl 6–2, 6–1 Emmanuelle Gagliardi / Janette Husárová defeated Olga Blahotová / Gabriela Navrátilová 6–3, 6–2