Japan contributed $100bn to the G20's $1.1 trillion pledge in loans and guarantees to developing countries, while China contributed $40bn.
"We will reform their mandates, scope and governance to reflect changes in the world economy and the new challenges of globalisation," summit leaders responded in a statement to a chief demand from Asian and other developing countries.
|Brown, right, said China and other countries were right to ask for a review of the IMF [EPA]
They added that such moves were needed to enhance the credibility and accountability of the IMF and other institutions.
"I believe people will be encouraged by the fact that China and India and Japan and many countries ... we've all been able to come together in a way we could never have done even a year or two ago and designed quite detailed proposals that will reshape the global financial system," Gordon Brown, the British prime minister, said.
He said China and other countries were right to ask for the representation and the quotas of the IMF to be changed to meet new challenges.
"We have set a timetable for doing that," added Brown.
Al Jazeera's Melissa Chan, reporting from Beijing, said the Chinese leadership had been vociferous about what they were unhappy with in terms of the global financial crisis.
And this was especially evident in the last few days when they had confidently and clearly expressed their views, taking more of a leading role in global finance, our correspondent said.
In welcoming the shift, Osamu Sakashita, deputy cabinet secretary for public relations for Taro Aso, the Japanese prime minister, said there was still "more to be done in that direction".
"We have long called for increasing representation of emerging economies," Sakashita said. "This is finally taking place, but only very slowly.