Sexy siblings!

Hilary and Haylie Duff showed off their curvy figures in revealing black swimsuits while vacationing in Mexico on Sunday.

Hilary, 23, chose a strapless look with an intricate string design in the back. Her sister, 26, opted for something with a plunging front and cut outs at the sides.

Both girls wore their hair swept back into high buns and hung out by the pool while Hilary's husband of one year, hockey player, Mike Comrie, relaxed on a raft.

Last month the couple hit up the Island of Capri, Italy, where the actress posed in a teeny black bikini while Comrie, 30, took pictures of her in a lagoon.

How does Duff — who shot to fame on Disney Channel's Lizzie McGuire in 2001 — stay in such great shape?

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"I work with a trainer named Harley Pasternak and I do a lot of Pilates," she told Us Weekly in April. "I'm just like everyone else. I go through stages where I feel super motivated and want to work out every day, and then I won't work out for two or three weeks and I'll feel like s**t. Then it's time to hop back on the wagon again!"

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