Traffic at Delhi's airport overtook Mumbai's – traditionally the country's busiest airport – in 2009.
Total passenger traffic at Indira Gandhi International Airport was 25.25 million flyers against 24.80 million at Chhatrapati Shivaji International Airport, government figures show.
In 2008, Mumbai was ahead with 24.33 million against Delhi's 23.24 million.
"Delhi has developed faster than Mumbai. Satellite towns like Gurgaon and Noida are generating huge traffic," said Tulsi Keshwarni, aviation expert.
"Mumbai, in contrast, has lost traffic with international airports coming up in Bangalore, Hyderabad, Thiruvananthapuram, Cochin and Goa."
"Delhi has changed from being merely a point of entry into India to a ‘business' destination like Mumbai," said Jean-Philippe Benoit, South Asia head of Swiss International Airlines.
The growth is not without its downside — congestion leading to more delays.
With the new integrated terminal opening in July, Delhi's traffic is expected to grow even higher at 10 per cent a year.