We've said it before and we'll say it again: Kourtney Kardashian is one hot mama.

In a sneak peek at an upcoming episode of Keeping Up with the Kardashians, the oldest Kardashian shows her younger sisters how it's done by stripping down to just her birthday suit for a sexy photo shoot in Costa Rica.

In the episode promo above, Kylie Jenner, Kim Kardashian West, Khloé Kardashian watch in awe as the 38-year-old mother of three flaunts her incredible curves in the pool while photographer Mike Rosenthal gets it all on camera.

VIDEO: Kourtney Kardashian Shows Off Bikini Body on Vacation

"Kourt, you are giving life right now!" hairstylist Jen Atkin cheers as Kourtney works her sexiest poses.

"I honestly was worried about you after Penelope," Khloe tells her later in their confessional. "I did think, like, she's gone. Now, she's YOLO-ing it up, f—ing bomb-ass body, naked in the pool, and your sisters should be afraid of you."

The youngest Kar-Jenner apparently feels the same way.

"What the f—!" the 19-year-old cries after glimpsing one particularly sexy shot. "I want to get in. I'm so jealous!"

Get it, girl!

Watch it all go down in the teaser above, and catch the entire episode of Keeping Up with the Kardashians Sunday at 9 p.m. ET, on E!.