The academy's board said it voted Tuesday night to oust both men who have been accused of sexual violence. The move comes months after it gave the boot to producer Harvey Weinstein, who has been accused of harassment and abuse by dozens of women.
"The board continues to encourage ethical standards that require members to uphold the Academy's values of respect for human dignity," the academy said in a statement, announcing the expulsion of Polanski and Cosby.
Polanski, 84, won the academy's Best Director Oscar in 2003 for his Holocaust drama The Pianist.
The French-born filmmaker did not collect his Oscar in person at the Los Angeles gala because a warrant was out for his arrest in connection with the 1977 sexual assault of a girl, who was 13 years old at the time. He pleaded guilty to the offense decades ago, but fled the United State before he could be sentenced.
Despite the widespread media coverage of the case, Harrison Ford announced Polanski was voted Best Director at the ceremony and celebrities such as Weinstein, Meryl Streep, Martin Scorsese, Jack Nicholson, Adrien Brody and Nicolas Cage stood and applauded. Polanski's other films include Rosemary's Baby, Chinatown, Frantic and The Ghost Writer.
Former German actress Renate Langer told The New York Times last fall that Polanksi raped her in February 1972 when she was 15 years old. Polanski's lawyer said the director has no knowledge of the alleged incident.
Cosby, 80, was convicted last week on three charges of aggravated indecent assault for drugging and assaulting Andrea Constand in 2004 at his home outside Philadelphia. He pleaded not guilty to the charges and his first trial ended last June with a hung jury.
More than 60 women have accused the former television titan of assaulting them in alleged incidents going back decades.
Camille Cosby is standing by her husband and Thursday asked for a criminal probe of the prosecutor in his criminal case.