The Titanic costars chatted outside DiCaprio's villa before heading to his foundation's annual fundraising gala in Saint-Tropez, where he raised $30 million.
DiCaprio, 42, showed off his tan upper body as he walked around shirtless in a pair of navy, patterned swim trunks.
Winslet, 41, rocked a salmon-colored bikini, a white cover-up and large black sunglasses.
The Wolf of Wall Street actor wrapped his arm around his longtime friend on his porch.
Though fans would likely love to see a real-life romance between DiCaprio and Winslet, she has been married to Ned Rocknroll since 2012. In fact, a source told Us Weekly at the time that DiCaprio walked the bride down the aisle at the private ceremony in New York City.
The Oscar-winning actress has three children: Mia, 16, Joe, 13, and Bear, 3. She shares Mia with her first husband, Jim Threapleton; Joe with her second husband, Sam Mendes; and Bear with Rocknroll.
DiCaprio, who most recently dated model Nina Agdal, also costarred with Winslet in the 2008 romantic drama Revolutionary Road, which was directed by the actress' then-husband Mendes.