The Underworld actress posted her statement to Instagram with a picture of her as a teenager.
Ms Beckinsale wrote that when she was called to meet Mr Weinstein at the Savoy Hotel in London, he opened the door in a bathrobe.
"I was incredibly naive and young and it did not cross my mind that this older, unattractive man would expect me to have any sexual interest in him," she wrote.
She left the room "uneasy but unscathed" and said that "a few years later" Mr Weinstein could not remember if he had tried anything with her at that first meeting.
Ms Beckinsale declined invitations to work on Miramax productions several times over the following years, a move she said prompted Mr Weinstein to reportedly call her vulgar names and threaten her.
"It speaks to the status quo in this business that I was aware that standing up for myself and saying no to things...undoubtedly harmed my career."
The Van Helsing actress said though that made her feel more empowered, it was not a decision supported by colleagues in the industry.
She also detailed an incident in which a male friend had warned another young, female actress who had a dinner meeting with Mr Weinstein. Unfortunately, the kind gesture backfired. Mr Weinstein was "sleeping with" the actress and reportedly barred Ms Beckinsale's male friend from working on another Miramax production.
She called on the industry to create a "new paradigm" as a result of the allegations against Mr Weinstein becoming public.
"Let's stop allowing our young women to be sexual cannon fodder," Ms Beckinsale pleaded with others in the film industry.
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