Friends of Zhao Ziyang's family said they were notified of the death of Liang Boqi at Beijing Hospital on Wednesday night. No cause of death was given.
Zhao helped promote reforms that launched China's economic boom but was purged after he called for compromise and expressed sympathy for some of the students' demands during the protests.
He was accused of splitting the party and placed under house arrest after the military crushed the protests.
Zhao died in 2005 at age 85.
Chinese scholar Wu Jiaxiang expressed regret that Liang did not see her husband's political rehabilitation before her death.