Subrata Roy has been in Tihar Jail for more than two years in relation with a long running dispute with markets regulator Sebi.
A Sahara group spokesperson said in a statement that Chhabi Roy has been the "guiding light of Sahara India Pariwar and departed for her heavenly abode at 1.34 am today".
"She has been critically ailing for last two years and was at a makeshift hospital at Sahara Shaher, Lucknow," the statement said.