No dollar figure or percentage were disclosed.
They became the first female African-Americans to hold an ownership stake in an NFL team when Dolphins majority owner Stephen Ross announced the move Tuesday.
"They have a total passion for winning, business, and philanthropy and are passionate Miami Dolphin fans," Ross said at news conference.
"We are just really excited to be a part of such a wonderful franchise, and Venus and I love the Dolphins," Serena said.
The tennis superstar siblings, who are full-time residents of Palm Beach Gardens, Fla., and natives of Lynwood, Calif., have combined for $50 million in earnings with 62 singles titles, nine grand slam doubles victories and five Olympic medals. It wasn't disclosed how much they invested in the Dolphins or the percentage they now hold.
They joined singer/entertainers Gloria and Emilio Estefan, Marc Anthony and Jennifer Lopez this year in expanding Miami's multi-cultural ownership organization.