They said Mr Saleh was believed to have transferred much of the wealth abroad under other names.
Yemen is the poorest country in the Middle East. It is in political turmoil, with Mr Saleh widely thought to retain a key role behind the scenes.
Mr Saleh has in the past denied allegations of corruption.
He was Yemen’s leader for 33 years before being forced from power in one of the 2011 Arab uprisings.
The report said Mr Saleh’s assets included property, cash, shares, gold and other valuable commodities spread across at least 20 countries.
“The origin of the funds used to generate Ali Abdullah Saleh’s wealth is believed to be partly from his corrupt practices as president of Yemen, particularly relating to gas and oil contracts,” it says.
Illegal activities produced private gain amounting to “nearly $2 billion a year over the last three decades”, it alleges.
“Many have argued that the country’s spiralling debt and economic problems would be alleviated with a repatriation of these alleged stolen assets,” the report noted.
It was authored by a panel of experts who monitor UN sanctions on Yemen.
The security situation in Yemen deteriorated sharply after President Abdrabbuh Mansour Hadi resigned in January following a takeover by a Shia militia group, the Houthis.
The UN experts said Mr Saleh, with the backing of large parts of the army, had “colluded with the Houthis in what resulted in a coup d’etat” against Mr Hadi.
Source: bbc.com/news/world
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