Mario Bermejo Castanedo is a Spanish footballer who plays for Celta de Vigo in the Spanish second division, as a striker.

In his early years, Bermejo played one game each in La Liga with Racing de Santander and Athletic de Bilbao, and then went on to represent sides in the lower leagues, on loan. His official debut with the latter came in a 1997–98 UEFA Cup match at U.C. Sampdoria, playing the final 30 minutes in the place of Ismael Urzaiz, in an eventual 2–1 win; he was eligible to play for the Basque due to his father's roots.

In 2002–03, definitely released by Athletic, Bermejo returned to the top level, but struggled to find the net the entire season for Recreativo de Huelva, which would befall again in next season's Segunda División. However, in 2004–05, he was instrumental in helping Racing de Ferrol maintain its league status, ending the season as the league's topscorer, at 25 - this included four past UD Almería in a 6–1 away win, Ferrol's biggest win ever in the second level.

The following seasons were also spent in the second level, with Albacete Balompié and Almería. With the latter, he scored five league goals, helping the Andalusia outfit to its first ever top division promotion.

After a season-long loan spent with Polideportivo Ejido, Bermejo was released and joined another side in the region, Xerez CD. His first season was highly productive both collectively (promotion, also a first ever) and individually (12 league goals, third-best in the squad, to Momo's 17 and Antoñito's 13), and the player, aged 30, penned a new two-year link at the season's close.

In the 2009–10 season, Xerez was immediately relegated back, but fought valliantly until the last rounds. Bermejo ranked amongst the league's topscorers at 12, namely netting in the last minute against Almería (2–1 home win), on 1 May 2010.