The actress already has a seven-year-old son, Stellan, with her English actor husband Paul Bettany.
And the 40-year-old has another child, Kai, 13, from a previous relationship with photographer David Dugan.
Now a representative for Jennifer says she is expecting a third baby in the new year.
The source told US Magazine about her and Paul’s wonderful news, just days after the star celebrated her milestone birthday.
Jennifer and Paul got married in 2003 after they met on the set of acclaimed film A Beautiful Mind.
The secret ceremony took place in Scotland and her first child with him was born that year.
Paul has previously spoken about his love for both kids and joked that he tries to impress them whenever he can.