Ashton Kutcher has resigned as chairman of the board of Thorn, the anti-child sex abuse organisation he co-founded in 2009.
His wife Mila Kunis, who served as an observer on Thorn's board, is also stepping down, Time magazine report.
It comes following widespread condemnation of their letters of support to their That 70s Show co-star, Danny Masterson, who was recently convicted of raping two women.
In a letter to the organisation, Kutcher said the letters that he and his wife wrote were an "error in judgement".
"Victims of sexual abuse have been historically silenced and the character statement I submitted is yet another painful instance of questioning victims who are brave enough to share their experiences," he said.
"After my wife and I spent several days of listening, personal reflection, learning, and conversations with survivors and the employees and leadership at Thorn, I have determined the responsible thing for me to do is resign as chairman of the board, effectively immediately."
The stars were hit with a backlash after the letters, which asked the judge for leniency when sentencing Masterson, were made public.
In his letter, Kutcher had described Masterson as a "dedicated and loyal" husband and father.
In her letter, Kunis wrote: "Throughout our time together, Danny has proven to be an amazing friend, confidant, and, above all, an outstanding older brother figure to me."
The pair later said "sorry" in a video, saying they didn't mean to "undermine the testimony of the victims" and apologised if they had "retraumatised them in any way".
Kutcher and Kunis met Masterson on That 70s Show.
Masterson was found guilty of raping two women and sentenced to 30 years to life behind bars.