74-year-old Hazare flew from Pune and reached the Delhi airport at around 1:30 am. He was taken to Medanta Hospital in adjoining Gurgaon.
Hazare will undergo a "detailed medical check-up" as he was suffering from persisting cough and back-pain, his close aides said.
The 74-year-old anti-corruption crusader was treated for acute bronchitis at Sancheti Hospital here earlier this month after he called off his three-day hunger strike for a strong Lokpal Bill midway.
Earlier, after calling off his 12-day hunger strike in Ramlila Maidan in August last year, Hazare had gone to Medanta for treatment.
The doctors led by Naresh Trehan had also constantly monitoring his condition during the Ramlila agitation.
Hazare`s health condition has forced him to call off the jail bharo agitation and prevented him taking a tour of the five poll-bound states.
However, he has said that he will embark on a nation-wide tour soon after he recovers from his illness during which he will "awaken" the people on the issue of corruption, he said he will not speak about indulging in violence.
"Soon after I regain my health, I will embark on an all- India tour. Then the corrupt people will understand that the allegations they level against me will not have an effect on people," he said.