The "Bourne" trilogy actor and wife Luciana, 32, are expecting their second child, Damon's representative, Jennifer Allen, said Monday.
"The couple is very excited," Allen said.
She said she did not have further details, including a due date for the baby.
Damon, 37, met Luciana — who debuted her baby bump at Sunday's Empire Film Awards in London — while she was working as a bartender in Florida. They tied the knot in December 2005 in New York during a private ceremony attended by the bride's daughter, Alexa, then 7, from a previous marriage.
They later welcomed a daughter, Isabella, who was born in June 2006.
The Oscar-winning co-screenwriter of 1997's "Good Will Hunting," Damon has carved a niche as an action star with the "Bourne" films and is now filming the CIA drama "Green Zone" in Morocco.
His screen credits also include roles in "Saving Private Ryan," "The Talented Mr. Ripley" and "Syriana."