The couple has two sons together, 5-year-old Oscar and 3-year-old Felix, reported People magazine online.
"Gillian Anderson and her partner Mark Griffiths have amicably separated after six years together," Anderson's representative said.
This is not the first serious relationship that has ended for Anderson.
In 1997, she had split from her husband Clyde Klotz, with whom she has a daughter, and in 2006 she parted ways with her second husband Julian Ozanne.
