The 34-year-old reality star -- who welcomed her first child, baby girl True, with Tristan Thompson in April -- couldn't seem to get enough of her sister's hotness, leaving an epic compliment in the comments.
In the photo, which was taken during Kim's recent appearance at the opening of her KKW Beauty & Fragrance pop-up in Los Angeles, the mother of three rocked a sexy, cleavage-baring ensemble with strappy heels and gold jewelry.
"Day Dreaming," wrote Kim, who shares North, 5, Saint, 2, and Chicago, 5 months, with husband Kanye West.
Khloe raved over the look, commenting, "So I don't get what's happening here."
"After three kids is there a secret rule that moms get hotter?" she continued. "You and Kourt are really making me think about the three kid rule."
Khloe's oldest sister, Kourtney Kardashian, is also the mother of three kids -- Mason, 8, Penelope, 5, and Reign, 3 -- with her ex, Scott Disick, and has been looking fit and fabulous during all her recent PDA-filled trips with new beau Yones Bendjima.
Earlier this week, Khloe revealed via Snapchat that she feels "anxious" whenever she's away from True.
"Tomorrow is my first day back to work," she revealed. "I have missed a feeding here or there with True, but I've never missed multiple feedings in a day. So I have a ton of anxiety."