Both ladies showed off their toned physiques in black workout attire and flaunted their fabulous rears.
"Barging in on Kim's booty selfie," Kendall captioned the cute pic.
Kim appeared to be wearing just a sports bra, black and gray leggings and sneakers for her workout.
Meanwhile, Kendall rocked a pulled-up gray tank, headband and black-and-white pants.
The pic comes less than a week after Kim shared a workout photo of herself and bestie Blac Chyna.
The 33-year-old hot mama posed in a low-cut, cleavage baring sports bra and black leggings in front of her bathroom mirror.
"Getting right for the new year," the E! reality star captioned the shot.
But the skin-filled selfies didn't end there…
Kim also posted a pic of the two ladies behind the back, proudly showing off their plump posteriors.
The blond beauty has credited the majority of her post-baby weight loss to the Atkins diet, saying that the low-carb program helped her get her body back.
That was extremely evident when she posed in a now-infamous swimsuit selfie back in October.
Friday morning, Kim lashed out at reports via Twitter that she's undergone plastic surgery to shed the baby weight.
"It sucks when people make up surgery or photoshop lies when I am so disciplined & work so hard," she explained.
"Just trying to motivate others & show anyone struggling with weight they can totally achieve whatever they want if they are dedicated!"
Don't forget to watch the season premiere of Keeping Up With the Kardashians on Jan. 19 at 9 p.m., only on E!