The 78-year-old actor, who denounced predatory behaviour, claimed female actors had used sex to get roles in the 1960s, News.com.au reported.
"... But from my own experience, when I was starting acting in the early '60s, the director of the theatre I was working at showed me some photographs he got from women who were wanting jobs," he said while delivering a talk at the Oxford Union.
Some of the would-be stars had written "DRR - directors' rights respected - at the bottom of their photograph," he said.
"People have taken advantage of that and encouraged it and it absolutely will not do," the "Lord of the Rings" star said.
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McKellen lauded the courage of victims for coming forward with horrifying stories of sexual harassment, but said he was concerned about people being "wrongly accused".
"I assume nothing but good will come out of these revelations, even though some people get wrongly accused - there's that side of it as well," he said.
Several A-listers such as Angelina Jolie, Gwyneth Paltrow, Cara Delevingne, among others opened up about facing sexual harassment at the hands of Weinstein after The New York Times and The New Yorker expose in October.
McKellen, who is homosexual, added the timing Spacey chose to come out was not ideal.