The Royals also sent cash to the Rockies, who are expected to start De La Rosa on Saturday against the Dodgers. Colorado needed a starter after demoting left-handed rookie Franklin Morales to Triple-A Colorado Springs.
"It's a good opportunity for me," De La Rosa said. "It's nice to get back in the Major Leagues."
De La Rosa, since accepting an assignment to Triple-A Omaha, has a 3-0 record and a 1.64 ERA. He had given up 18 hits and just four runs in 22 innings, with 23 strikeouts and seven walks.
Although Coors Field, home of the Rockies, is known as not being pitcher-friendly, De La Rosa was not concerned.
"I pitched there before, and I liked it," he said.
His first start there will be against a fellow Mexican pitcher, Dodgers right-hander Esteban Loaiza.
De La Rosa had been rumored to be the player to be named in the deal that brought reliever Ramon Ramirez to Kansas City, but the Royals said there was no connection between that deal and this one. The Rockies still owe the Royals a player and vice versa.
Technically, De La Rosa's contract was moved from Omaha to Colorado Springs.
De La Rosa pitched two seasons for the Royals, compiling an 11-16 record and 5.64 ERA in 36 games (33 starts) in 2006-07. He was obtained from the Brewers on July 26, 2006, in exchange for infielder Tony Graffanino.
"I want to thank Kansas City for the opportunity they gave me the last two years," De La Rosa said.
During his stay with Omaha, De La Rosa said he benefited from the help of pitching coach Tom Burgmeier, a former left-handed pitcher.
During Spring Training, De La Rosa was unable to regain his job in the starting rotation and was designated for assignment on March 26.
In 97 Major League games, De La Rosa has a 15-23 record and a 5.85 ERA.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.