The Keeping Up With the Kardashians star and her partner Scott Disick are expecting their third child in December.
In the action shot which reality star shared with her eight million followers, Kourtney can be seen second from left wearing a metal grey bikini, as she and a group of four friends jump into a pool.
Kourtney and Scott have been together for seven years and are already parents to Mason, four, and Penelope, 23 months.
It was first reported at the beginning of June that the TV star is pregnant, with a source telling US Weekly: "Kourtney wants to have a handful of kids."
Kourtney confirmed the pregnancy during the premiere episode of the reality show's new season.
Kourtney Kardashian and Scott Disick
A friend confirmed that the couple don't know the gender yet, adding: "They just want the baby to be healthy."
Her mum Kris Jenner and sister Kim Kardashian had both confirmed to fans that the pregnancy would be addressed on the premiere.
"Kourtney will also be addressing pregnancy rumours this Sunday on our premiere!" Kim wrote on Twitter. "So be sure to tune in! #keepingupwiththeKardashians."
The brunette beauty has been pushing ahead on the career front recently, opening a new Dash store in the Hamptons with sister Khloé. The whole experience was filmed for a new Keeping Up With The Kardashians spin-off show.
Khloé took to Instagram to share the exciting news. "Dear Southampton, we are now open. Thanks for having us this summer!" the image read. Kourtney then reposted the picture.