The figure was slightly lower (83%) for those working in broadcasting.
Brand has been investigated by the police, the BBC, Channel 4 and Banijay.
He vehemently denies all allegations and claims against him and says all relationships were consensual.
Russell BrandJeff Spicer/Getty Images
A number of freelancers spoke anonymously for the survey.
Bectu Head Philippa Childs said: Its no secret that sexual harassment remains a scourge on the creative industries.
The research comes as Bectu rolls out a helpline for members who experience sexual harassment at work.
Members can use the service to record their experiences and so help the union to track problem areas.
