The 30-year-old Castillo is heading to Minnesota for hard-throwing reliever Travis Bowyer and Scott Tyler, who can start or relieve.
Castillo is the latest cost-cutting move by the Marlins, who are streamlining their payroll now that their stadium efforts in downtown Miami have fallen through.
"Luis Castillo has been a tremendous player in this organization for a long time," Marlins general manager Larry Beinfest said. "He's an All-Star, a Gold Glover, a world champion. Obviously, it was a tough trade to make but necessary, given our market correction to our payroll. We're excited about the young players coming back."
The Marlins continue to stockpile pitching. Bowyer throws 98 mph, and he projects as a possible closer. Bowyer is a power pitcher who went to the Arizona Fall League to refine his breaking pitches and slider. In the AFL, the right-hander was 0-2 with a 9.39 ERA with one save in 10 games. He did strike out 19 while walking two in 15 1/3 innings.
In a brief stint with the Twins, Bowyer was 0-1 with a 5.59 ERA, striking out 12 with three walks in 9 2/3 innings. And he posted a 4-2 record with a 2.78 ERA and 23 saves in 74 1/3 innings at Triple-A Rochester this season.
Tyler went 7-8 with a 3.95 ERA for Fort Myers in the Florida State Class A League.
"Bowyer is a big right-hander with a 98 mph fastball," Beinfest said. "We think he's going to fit right into our bullpen and into our future. Scott Tyler will go into our system, and we also think he has a bright future as a starter in the organization."
About Bowyer, Beinfest said: "That was the thought when we acquired him, that he is a future closer. We think he has the stuff to do it."
A three-time All-Star and reigning three-time Gold Glove winning second baseman, Castillo was signed by the Marlins out of his home in Santo Domingo, Dominican Republic, in 1992.
The switch-hitting second baseman played in 75 games for the Marlins' 1997 World Series championship team, and he was an All-Star and Gold Glove winner on the 2003 World Series championship squad.
Beinfest broke the news to Castillo early Friday afternoon. The deal had been in the works since shortly before Thanksgiving.
"Obviously, it was a tough phone call," Beinfest said. "He will do fine. We wish him well and thank him for everything."
Castillo hit .301 in 122 games in 2005, and he has a career average of .293. He is the Marlins' all-time leader in numerous categories, including games played (1,127), triples (42), walks (532), hits (1,272) and stolen bases (281).
In 2002, Castillo hit safely in 35 straight games, which was the longest hitting streak in the Major Leagues since 1987 until Jimmy Rollins of the Phillies topped that mark by hitting safely in 36 straight games when the season ended.
With Castillo traded and shortstop Alex Gonzalez expected to leave through free agency, the Majors' longest-running double-play combination is being broken up. Castillo and Gonzalez started 715 games together, while second-place tandem Rafael Furcal and Marcus Giles of Atlanta aren't yet at 400 games. Castillo and Gonzalez combined for 356 doubles plays, including 52 in 2005.
Castillo is set to make $5 million in 2006, and he has a team option for $5.75 million in 2007.
With the Winter Meetings set to begin next week in Dallas, the Marlins already have moved many key players, including Josh Beckett, Mike Lowell, Carlos Delgado, Guillermo Mota and now Castillo.
Beinfest noted that the club will remain active through the Winter Meetings, and speculation is growing that center fielder Juan Pierre and catcher Paul Lo Duca will be dealt by the end of next week.
The Yankees already have expressed interest in Pierre. And Lo Duca has attracted attention from the Diamondbacks, Rockies and Mets. Lo Duca is set to earn $6.25 million, and Pierre is in line to make about $5.5 million through arbitration.
"At this point, we're not going to respond to trade rumors," Beinfest said. "We've been very active. We're going to remain active. We're bringing our complement of people to Dallas. We'll look at achieving what we need to achieve, and we're going to try to get the ballclub fortified for the regular season.
"We still do have a plan of action as we head to Dallas, and we're going to follow through on it."
With payroll dipping from a franchise-record $65 million in 2005 to closer to $30 million for next season, Beinfest pointed out he is following through on a directive to groom the franchise for the future.
Castillo's departure creates an opening at second base for the Marlins. Beinfest noted that internally, the club is considering converted shortstop Josh Wilson. Robert Andino, called up in September to play shortstop, could be moved to second now that the club has obtained prospect Hanley Ramirez from the Red Sox to play short. Recently signed journeyman Alfredo Amezaga also will get a chance.
Beinfest, however, didn't rule out acquiring a second baseman in either a trade or a modestly priced free agency signing. Veterans like Rich Aurilia would fill that description.
"I wouldn't rule out reasonable free agency or trade to fill the second-base spot," Beinfest said.
Formerly a leadoff hitter, Castillo batted second most of the past three seasons after Pierre was acquired after the 2002 season from Colorado.
Last season, Castillo's health became an issue as he was plagued by hip and quadriceps problems. The injuries greatly reduced his threat to steal, as he swiped only 10 bases in 17 attempts.
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.