Economic growth of recent decades had benefitted the rich more than the poor in Germany and other developed nations, the OECD said in the survey entitled "Growing Unequal: Income distribution and poverty in OECD countries."
Germany, Canada, Norway and the United States were most affected by the widening gap between rich and poor, while Greece, Mexico and Britain had seen a shrinking gap, the study found.
"The gap between rich and poor has grown in more than three-quarters of OECD countries over the past two decades," said the OECD, an influential policy forum for 30 top world economies.
Presenting the report at a news conference in Berlin, one of the study's co-authors, Michael Foerster, said child poverty had risen in countries such as Germany, the Czech Republic, Canada and New Zealand. But child poverty was lower in countries where a large percentage of women worked, Foerster said.
"The increase in child poverty deserves more policy attention than it is currently receiving in many countries. More attention is needed to issues of child development to ensure that no child is left behind."
In the report, OECD Secretary General Angel Gurria warned of the dangers posed by inequality and the need for governments to tackle it.
"Growing inequality is divisive. It polarises societies, it divides regions within countries, and it carves up the world between rich and poor," he said.
"Greater income inequality stifles upward mobility between generations, making it harder for talented and hard-working people to get the rewards they deserve. Ignoring increasing inequality is not an option."