The dismissal came one day after the Cubs finished their season with a 67-95 record, the second worst in the National League and the team's worst since 1980, not counting the strike years of 1994 and 1981.
"It came down to wins, winning games, and I did not win games," Riggleman said. "This is the result of being accountable for wins and losses."
Riggleman managed Chicago for five seasons after two years managing the San Diego Padres. He had one year remaining on a contract that was extended through the 2000 season last November.
Cubs general manager Ed Lynch said he decided to fire Riggleman more than a week ago.
"I felt it was something we needed to do," Lynch said.
"Sometimes a change is necessary to change the perception or attitude or direction of a club," he added. "I deserve a lot of the blame for what has happened here, and I accept that."
The Cubs plan to offer Riggleman another job in the organization but did not elaborate. Riggleman said he would consider it but hopes to manage again.
"I'd love to manage," he said. "If a good opportunity comes up, I would jump at it. I had a good opportunity here, and it didn't work out."
The team also fired four coaches and said Chicago Cubs great Billy Williams, the dugout coach, will be considered for the manager's job.
Riggleman had a 374-419 record with the Cubs, including two 90-game losers and one 90-game winner in the last three seasons.
Behind the power of Sosa, Chicago won the NL wild card in a playoff last season, prompting the Cubs to extend Riggleman's contract.
But a starting rotation that was also a big part of the success a year ago fell apart. Rookie of the Year Kerry Wood blew out his elbow in spring training; 15-game winner Steve Trachsel became an 18-game loser in 1999; and staff ace Kevin Tapani, who won 19 games a year ago, was hit by injuries, finishing the season on the disabled list with a 6-12 record.
The Cubs, who won only 26 games after the July All-Star break, plummeted after being nine games over .500 in early June, and Riggleman could do little to help.
Speculation began to build on whether Riggleman would last the season. General manager Ed Lynch finally said in August that their 46-year-old manager would be evaluated after the season. And the Cubs wasted little time.
Some players, including star first baseman Mark Grace, came out in support of Riggleman as did several managers, Tony La Russa of St. Louis and Jerry Manuel of the White Sox.
Riggleman admitted the season had damaged the spirit of his team and changes would be forthcoming, maybe including him.
"As I've said many times before, it's not the cure for cancer, the way to world peace," Riggleman said. "There are a lot of tough things going on in the world, and whether the manager comes back is pretty low on the list of priorities."
Also fired today were pitching coach Marty DeMerritt, third-base coach Tom Gamboa and first-base coach Dan Radison, although the Cubs said they would be considered for positions after a new manager is hired. Bullpen coach Dave Bialas also was fired but will be offered another position. Hitting coach Jeff Pentland will be retained.
Riggleman was characterized as mild-mannered but fair, a manager who would stand up to his players if needed, as he did in the 1997 season finale in St. Louis when he confronted Sosa in the dugout for what he thought was selfish play.
That was before Sosa went on to become one of the great home run hitters in baseball history the past two seasons with 66 and 63 homers. The two patched up their differences.