Anna Hazare was admitted in the intensive care unit of a private hospital in Gurgaon on Friday morning after he complained of acidity and weakness.
According to an official of Medanta-The Medicity, the 75-year-old social activist was brought in at 10am.
"Hazare complained of nausea, acidity and was throwing up. He was diagnosed for gastritis," said the hospital source on condition of anonymity.
"He is likely to be discharged on Saturday," he added.
The social activist's aide Kiran Bedi and anti-graft leader Arvind Kejriwal broke the news of his ill health on a social networking website.
"Anna is admitted in Medanta and under intensive care of a team of doctors. What are the health issues only doctors can say as professionals!" Bedi said around noon on Friday.
Former Team Anna member Arvind Kejriwal also confirmed Hazare's admission to the hospital on a social networking website.
"Anna in hospital. I wish I cud go to see him. I wish him fast recovery," he said around the same time.
Kejriwal recently launched a political party, Aam Aadmi Party, after parting ways with Hazare.
He was admitted at the hospital in January for hypertension.