The two first met in 1997 on the set of Winslet's Titanic follow-up film Hideous Kinky, on which Threapleton served as assistant director. They later married in 1998.
Winslet, 25, and Threapleton, 26, have one daughter, Mia, aged 9 months.
"No other parties are involved in this amicable and respectful separation," said Winslet's spokesman, Robert Garlock. "Their daughter Mia will remain the first priority for both of them."
