Sofia, 20, sported a skimpy yellow floral bikini and large black sunglasses.
Scott, 36, donned a navy blue tee shirt, black shorts and brown shades.
Kylie's BFF Stassie Karanikolaou and the couple partied on a yacht and made a splash as they jumped into the sea.
The young billionaire will turn 22 on Saturday, August 10.
Sofia and Stassie were also spotted later on in the day, riding a jet ski together and swimming in the ocean.
After the group took a swim, they met up with Kris Jenner and Travis Scott and took a stroll around the seaside town of Positano.
Kylie reportedly rented out a $250 million, 300-foot yacht, called Tranquility for her lavish birthday celebrations.
What are your thoughts on Scott and Sofia's Capri vacation? Sound off in the comments below!