Oxfam said that President Joko Widodo had failed to fulfil pledges to fight inequality and called on the government to urgently increase spending on public services and make corporations and the wealthy pay more tax.
Indonesia has enjoyed an economic boom that has reduced the number of people living in extreme poverty but the gap between rich and poor has risen faster than in any other Southeast Asian country in the past 20 years, AFP quoted the Oxfam study as saying.
"The benefits of growth have not been shared equally, and millions have been left behind," said the research, which was released earlier this week.
In 2016, the collective wealth of the four richest Indonesians, all men, was $25 billion, Oxfam said. This was more than the total wealth of the 100 million poorest, out of a population of 255 million, it said.