Saha joined United from Fulham in January 2004 for £12.8 million.
Saha told United’s website: “I am really enjoying my time here.
“I want to show my commitment to Manchester United and repay the faith that they have shown in me.”
Manchester United boss Sir Alex Ferguson said: “I’m delighted we have extended Louis’ contract.
“We’re happy to see Louis here until at least 2010 and to add him to the players who have recently signed new contracts.
“Hopefully we’ll have an exciting end to the season and add some silverware.
“We address the situation of players’ contracts now and then in order to strengthen the club and it’s great to add Louis to the list.
“His form has been fantastic since he has come back from injury and he has scored 26 goals in that time.”