The group, which included models Hailey Baldwin and Bella Hadid, spent the day soaking up the sun on the beach and sailing in the crystal clear waters on a luxury yacht, plus documenting it all on Instagram of course.
Kylie shared a number of enviable snaps from the beach,telling fans she was having the "time of my life" with her friends.The 19-year-old appeared to be having fun as she played in the sea with her sister Kendall while wearing a red bikini and gold chain body jewellery.
"Thanks for all the birthday wishes. Best birthday yet," she captioned one photo of herself standing on the yacht.
The rest of the group appeared to be enjoying the trip just as much, taking the opportunity to do some sunbathing and strike a pose with the tropical turquoise waters providing the perfect backdrop.
Bella, 19, showed off her model physique in a frayed denim bikini, adding gold hoop earrings, a choker and chain necklace to add glamour to her beach side look.
The younger sister of Gigi Hadid wished Kylie a happy birthday by sharing a photo of her friend running towards her on the beach."Happy birthday Ky Baby… life would be boring without you," she captioned the snap.
The incredible celebrations didn't end there; Kendall arranged a special surprise for her sister at the end of the day by arranging a fireworks display on the beach. The 20-year-old shared a video of the display with fans, in which she can be heard saying: "Happy birthday sister, I love you!"