"She died early this morning. She was 66," her agent Mats Nilemar said.
Nyman got her breakthrough in Vilgot Sjöman's 1967 and 1968 landmark films "I am Curious (Yellow)" and "I am Curious (Blue)" based on the colours of the Swedish flag.
Nyman was awarded the Swedish Film Institute's Guldbagge award for Best Actress
in 1968 for her work in both films, which had caused scandal because of her nudity.
"I am Curious (Yellow)" evoked moral indignation in the United States for its numerous scenes of staged sex, including one scene when Lena kisses her lover's flaccid penis, and was banned in Massachusetts for being pornographic.
The ban was later overturned after the Supreme Court ruled that the movie was not obscene. She also played Ronja Rövardotter's mother Lovis in the 1984 adaptation of Sweden's beloved Astrid Lindgren novel by the same name.
Nyman made her film debut in 1955, going to land roles in over 30 films of note during a career spanning over 50 years. Tributes to the actress poured in in Sweden on Friday, where she is known for her work in theatre, film and television.
"Her unique style and characteristic expression has really served to broaden how a woman can act and be presented on stage," said Johanna Skobe at Women in Swedish Performing Arts to The Local on Friday.