He accepted a glass of fruit juice from a five-year-old girl.
His move came a day after MPs expressed support for proposed changes to anti-corruption legislation.
After nearly nine hours of debate, Finance Minister Pranab Mukherjee told parliament the "sense of the House" was behind Anna Hazare's key demands.
However, an expected vote on the proposals did not take place.
Mr Hazare, 74, had vowed not to stop until a tougher bill was passed, but doctors have warned that his health is deteriorating rapidly.
He has so far lost 7kg (15lbs) in weight and has refused medical advice to be put on an intravenous drip to help him rehydrate.
Opening Saturday's debate in Delhi on the proposed amendments, Mr Mukherjee said India was "at a crossroads", with the focus squarely on the country's parliamentary democracy.
Mr Mukherjee said that while there was support for Mr Hazare's proposals, a solution would have to be found within the Indian constitution.
Meanwhile, governing Congress party leader Rahul Gandhi said he had "serious doubts" that a single bill would end corruption.
Source: Anna Hazare: India campaigner ends hunger strike