"Grace and I have two beautiful children together," the Oscar-winning actor said in a statement to CNN on Tuesday. "We are entering a period of transition in our relationship that is a difficult but constructive process."
"I honor Grace as a wonderful mother and I ask for privacy and respect from everyone as we move forward to develop our roles as partners in raising children," De Niro added in the statement.
The couple met when Hightower was working as a hostess at a Mr. Chow restaurant and married in 1997.
They are the parents of two children, Elliott, 20, and Helen Grace, 6.
Hightower is a philanthropist who has also had minor roles as an actor in films and television.
The couple has had marital problems before. De Niro filed for divorce in 1999, but the two reconciled and renewed their votes in 2004.
The actor was previously married to Diahnne Abbott from 1976 to 1988 and they are the parents of two children, Drena, 47, and Raphael, 42.
In 1995 he received his twin sons, Aaron and Julian, with his girlfriend at the time, Touki Smith.