Mr Ambani and his wife are India's richest people
The number of billionaires in India doubled in 2009, Forbes magazine says.
It lists 49 Indian billionaires, up from 24 the previous year. India, which has many of the world's poorest people, also has 10 of Asia's top 25 richest.
The wealthiest Indian is Mukesh Ambani, worth an estimated $29bn. His Reliance Industries is India's largest firm.
Steel tycoon Lakshmi Mittal is second with $28.7bn. Both are in Forbes' list of the 10 richest men in the world - Mr Ambani at four, Mr Mittal at five.
Mexican telecom giant Carlos Slim ($53.5bn) came top - the first time since 1994 that an American has not led the rankings - ahead of Microsoft founder Bill Gates ($53bn) and US investor Warren Buffett ($43bn).
Forbes listed 1,011 billionaires, up from 793 last year but still below the 1,125 listed in 2008.
The improving health of the global economy meant that 55 countries were represented - with Pakistan (clothing exporter Mian Muhammad Mansha, number 937) and Finland (Antti Herlin, number 773) adding their first billionaires.
Strengthening stock markets and several large public offerings during the past year helped Asia close the gap with Europe.
A total of 234 Asian billionaires were featured in the 2010 list compared with 248 from Europe.
The country with most billionaires is the US, with 403. But China comes second with 64 living in the mainland.