Witherspoon, who turns 40 on March 22, jetted off to Cabo San Lucas, Mexico for a 'girls trip' just weeks before the milestone occasion.
The mother of three flaunted her toned body as she lounged poolside with friends. She was all smiles as she sipped on water and relaxed in the sun, donning a sexy red one-piece swimsuit that featured cutouts down her chest.
She accessorized her beach-ready look with white cat-eye sunglasses and a matching wide-brim hat.
Earlier in the week, Witherspoon showed off even more cleavage, stepping out in a black one-piece swimsuit with a plunging halter neckline.
Witherspoon seems to be enjoying the much-deserved time off in the tropical getaway hotspot. On Wednesday, she posted a picture of a colorful bouquet of flowers to her Instagram.
"#Prettyinpink," she captioned the shot with a few flower emojis. Later she shared a view of Cabo from her plane ride writing, "Here comes paradise #cabo."
Along with her birthday, Witherspoon will also celebrate her fifth wedding anniversary with her husband, Jim Toth, later this month.