Rojas turned professional in 1985 and captured the WBA flyweight title with a decision win over Fidel Bassa in 1989. He lost the title in his first defense to Yul-Woo Lee by decision in 1990. Later that year he took on Leopard Tamakuma again for the WBA flyweight title, but drew with him.
He later moved up in weight and challenged WBA super flyweight title holder Yokthai Sithoar in 1997, but lost a decision. In 1998 he captured the WBA super flyweight title, with a decision win over Satoshi Iida. He lost the title in 1999 to Hideki Todaka and later retired in 2004 after a loss to Eric Morel.
