The BJP stalwart is admitted to the ICU of the cardio-thoracic centre at the hospital and has shown improvements in the last 10 days.
"He continues to show improvement and is being monitored by a team of doctors," an AIIMS official said.
The 93-year-old leader was admitted to the premier hospital on June 11 with a kidney tract infection, chest congestion and urine output on the lower side.
Prime Minister Narendra Modi, BJP chief Amit Shah, RSS chief Mohan Bhagwat, former prime ministers Manmohan Singh and HD Deve Gowda, Congress president Rahul Gandhi, Vice President Vankaiah Naidu and several chief ministers and union ministers have visited Mr Vajpayee at the AIIMS over the past 11 days.
Atal Bihari Vajpayee was thrice elected as the prime minister between 1996 and 1999 and is the only non-Congress prime minister to complete the full term of five years, from 1999 to 2004. As his health deteriorated, he slowly withdrew himself from public life and remained confined to his residence for years.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.