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 and was held from April 12 through April 18, 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 
- It was Chela's 2nd title of the year and the 4th of his career.
Émilie Loit defeated Iveta Benešová 7–5, 7–6(7–1) 
- It was Loit's 3rd title of the year and the 10th of her career.
Juan Ignacio Chela / Gastón Gaudio defeated František Čermák / Leoš Friedl 6–2, 6–1
- It was Chela's 3rd title of the year and the 5th of his career. It was Gaudio's 2nd title of the year and the 4th of his career.
Emmanuelle Gagliardi / Janette Husárová defeated Olga Blahotova / Gabriela Navrátilová 6–3, 6–2
- It was Gagliardi's 1st title of the year and the 1st of her career. It was Husárová's 2nd title of the year and the 17th of her career.