The Keeping Up With The Kardashians star arrived in her black Porsche and sported a sleek chocolate brown sports bra and leggings ensemble set by Set Active. She completed her gym look with a matching brown cardigan, tortoiseshell shades, small shoulder bag and Yeezy slides, which she wore with thick socks.
Joining her pal for the private Pilates session, the 24-year-old blonde beauty arrived separately, looking equally as fit, flashing her enviable abs in a black triangle top, black leggings fuzzy cardigan and hot pink slides.
Scroll though the gallery below to see more pics from the pals' active afternoon outing.
Friends for over a decade, Jenner and Bieber both come from famous families in Hollywood. Jenner is also tight buds with her pal's husband Justin Bieber.
"It keeps my mind and my body really healthy,' Bieber told Women's Health UK's "Going for Goal" podcast of Pilates. "I used to be a ballet dancer so Pilates for me gets my body personally in the best shape, because it's very elongating. A lot of the movements in Pilates are very similar to dance and I think that's why I identify with and like it so much."
Making sure to stay hydrated for her workout, Jenner was spotted carrying a giant blue canteen of water.
Jenner will soon as have even more time to workout as the 20th and final season of KUWTK is currently airing Thursdays, on E!.