The estimated figure for the end of 2016 is an increase of 300,000 on 2015, according to its annual report.
It is a smaller increase than 2014-15, when the figure rose by five million.
But the UN high commissioner for refugees Filippo Grandi said it was still a disheartening failure of international diplomacy.
"The world seems to have become unable to make peace," Mr Grandi said.
"So you will see old conflicts that continue to linger, and new conflicts erupting, and both produce displacement… forced displacement is a symbol for wars that never end."
In 2016, some 340,000 people fled the violence in South Sudan into neighbouring Uganda. That was more than any other country - even more than the 200,000 people estimated to have fled Syria.
Just 36 hours after crossing the border by a simple wooden plank bridge, refugees are given a small plot of land and the materials they need to start growing their own food.
A year ago, the village of Bidi Bidi was just that, but now it is one of the biggest refugee settlements in the world - home to more than a quarter of a million people and covering 250 square kilometres.
The UN said it hoped Monday's record breaking numbers of displaced would encourage wealthy countries to think again: not just to accept more refugees, but to invest in peace promotion, and reconstruction.
Mr Grandi also warned of the burden being placed on many of the world's poorest states, as some 84% of the world's displaced people are living in poor and middle income countries.
"How am I to ask countries with far less resources, in Africa, in the Middle East, in Asia, to take millions of refugees if the richer countries are refusing to do so?" he said.