Wilde made the announcement via Instagram on April 18 sharing a lovely picture showing her cradling her bump as she sat in bed with son, Otis.
The youngster, who turns two on Wednesday, April 20, cradled his own stomach in sympathy with his mother, who captioned the black and white snap: 'Matching baby bumps!'
The 32-year-old actress is currently on vacation in Hawaii with her son and husband, who is promoting his new animated "Angry Birds" movie, for which he voices a character. The trio were spotted at the beach over the weekend, with Tron: Legacy star Olivia keeping her stomach area covered in some denim dungarees.
Just last week Jason told reporters he wanted to expand his brood with his wife-to-be, joking that they decided they should after creating the perfection that is Otis.
Catch up with Olivia Wilde in the movie trailer below: