While Kardashian, 39, opted for a black string bikini, little sister Jenner, 22, chose a nude-colored off-the-shoulder bathing suit.
“Yin [and] Yang,” Kardashian captured the snap.
“The most gorgeous women I know! Love you both!,” their dad Caitlin Jenner commented.
Jenner also shared a solo shot of herself applying sunscreen.
“Wear your sunscreen,” she wrote to her fans.
Over the weekend, Kylie made headlines for posing in a bikini with a different sister.
Kylie and sister Kendall Jenner, 24, set hearts on fire with a playful snap showing off their fit figures in the sand.
The Kylie Cosmetics founder shared the photo with her 164 million Instagram followers of the siblings wearing matching lime green bathing suits.