Marco Antonio de Lima Ruas (born January 23, 1961) is a professional mixed martial arts fighter and instructor. He is famous for being the founder of Ruas Vale Tudo, a hybrid of Brazilian submission fighting and kickboxing; he has instructed fighters such as Pedro Rizzo and Renato Sobral.

Ruas competed in early Ultimate Fighting Championship events, winning UFC 7 in a classic fight against 6'8", 330lb Paul Varelans. He also faced down opponent Oleg Taktarov in UFC's Ultimate Ultimate, but lost via decision. Ruas would go on to a draw with Taktarov a year later, winning the WVC Super Fight belt in the process. He returned briefly to fight former heavyweight champion Maurice Smith in UFC 21, but lost not being able to continue due to an injury in his knee.

Marco's first recorded fight was in 1984.

Marco's nickname is "The King of the Streets" (Ruas actually means "Streets" in Portuguese).

Marco lives in Laguna Niguel, California and coached the Southern California Condors in the International Fight League before the organization's collapse.