Ambani, who heads the Reliance ADA Group, was questioned for two hours by members of the Public Accounts Committee over the 2008 sale of telecom licences to companies at throwaway prices, panel chairman Murli Manohar Joshi said.
Ambani's company, Reliance Telecom, a unit of Reliance Communications, has been charged by police in the case.
Ambani said that because the matter was before the courts, "he should not be asked anything that could be incriminate him," Joshi told reporters.
"He answered whatever questions we asked but when he sought immunity because of the court case, we agreed."
Joshi was referring to 80,000 pages of charges and documents linked to the case which were presented by state prosecutors in court on Saturday.
Former telecom minister A. Raja is standing trial in what has become known as the 2G spectrum scandal. He is suspected of bending the rules to favour certain companies in awarding mobile licences in exchange for kickbacks.
Three Reliance executives are due to stand trial in the fraud case, which has led to charges against Raja of abuse of power, conspiracy, cheating, forgery and criminal misconduct.
"Ambani spoke openly but at times he said he could reply to certain questions only after referring to documents," said the PAC chairman, a senior member of main opposition Bharatiya Janata Party.
The parliamentary panel, a permanent body comprising lawmakers and retired judges, is leading one of a number of investigations into the scam, potentially the biggest in Indian history.
The PAC also recorded evidence of senior executives of four telecom firms which are linked to the alleged fraud case, Joshi said.
The companies which got the 2G licences "were formed in apparent haste to enter the telecom sector and it appears they were aiming only for the (2G) licences," the committee chief said.
The telecom scandal has tarnished the reputation of Prime Minister Manmohan Singh's Congress-led government, and has also raised anxiety about corruption and its impact on business in India.
The national auditor has said the alleged 2G spectrum fraud may have cost the government up to $40 billion in lost revenues.
On Monday, the parliamentary watchdog questioned one of India's most respected business figures, Ratan Tata, who heads the Tata conglomerate.
The panel on Monday also quizzed an influential lobbyist, Niira Radia.
"You must wait and see what happens," commented Joshi when reporters asked if the committee would also summon prime minister Singh to appear.