Ambani, Reliance Industries chairman with $29 billion ranked fourth in the list, while Mittal, Chairman Arcelor Mittal, with a fortune of $28.7 billion has claimed the fifth place.
Forbes has described Ambani as the one of the 24 Indian billionares, all of whom barring one are poorer than 2009, adding that 29 billionares slipped from their billionaires status due to the 44 percent tumble in the India"s stock market, including 18 percent depreciation of Indian rupee against dollar.
Mexican telecom tycoon Carlo Slim Helu with $53.5 billion is the new topper on the list, by being $500 million ahead of Microsoft founder Bill Gates.
Gates, with $53 billion slipped to the second place, followed by legendary investor Warren Buffet who ranked third with $47 billion.
Four Indians figure among World's top 50 billionaires in the Forbes list.
Azim Premji, chariman of Wipor technologies ranked 28 with a fortune of $17.0 billion.
Shashi & Ravi Ruia brothers with $13.0 billion shared the 40th spot, while Savitri Jindal, head of O P Jindal Group , with a fortune of $12.2 billion secured the 44th position.