Greenglass, whose damning testimony was later called into question, died April 7 in New York where she had lived under an assumed name for more than four decades, the New York Times reported.
Her death was disclosed in court papers June 23, the day the federal government agreed to release secret grand jury testimony, 57 years after Julius and Ethel Rosenberg were convicted of conspiracy to commit espionage.
David Greenglass, Ethel Rosenberg's brother, had been recruited by Rosenberg to get information on the atomic bomb at the Manhattan Project where Greenglass worked.
Rosenberg eventually confessed to espionage but the case against his wife remained flimsy until David and Ruth Greenglass linked her to the spying activities by testifying she had typed the secret information notes supplied by her brother.
The Rosenbergs were executed on June 19, 1953.
Much later, Greenglass admitted in the book "The Brother: The Untold Story of the Rosenberg Case," that he had lied on the stand, that his wife probably had done the typing.