"(Director) Martin Scorsese kept saying, 'You're an actor playing a character called Katharine Hepburn.' I'm not up there doing my cabaret impersonation. That would be a grotesque," Blanchett told reporters.
Noting her job is to remind the audience of how Hepburn looked and sounded, the actress pointed out that audiences never really knew the "real" woman inside the movie star.
"We all know her as 'the creature,' as she called herself, the screen persona, because she was desperately, desperately private," she said.
Blanchett said playing the screen icon was a bit intimidating.
"Of course you panic because I'm trying to represent somebody in the same medium in which they were iconic, in which the audience rightfully feels a sense of ownership of her screen persona. But it's for Martin Scorsese. The script is extraordinary and it's an enormous challenge," she said.
"I'm not a fearful person and so if you say something is insurmountable, I'm likely to charge headlong towards it and give it a go."