The 27-year-old former 'Gossip Girl' actress announced her pregnancy news by posting a picture of herself showing off her baby bump on her Preserve lifestyle website, reported US magazine.
In the snap, Lively is shown cradling her bulging belly, while she dedicated the latest installment in her web project to expectant mothers and family.
A message posted on the page read, "The entire next month will be sprinkled with highlights for women in this exciting chapter of their lives. Congratulations to all the expecting mothers out there."
It was the first child for the 29-year-old blonde actress and her French journalist fiance Romain Dauriac.