The former oil tycoon, Mikhail Khodorkovsky, who is serving an eight-year prison term, was found guilty in his second trial, which would keep him behind bars for several more years.
A judge who started reading his verdict on Monday said Mr. Khodorkovsky (47) was guilty of stealing oil from his own company and laundering the proceeds.
Prosecution has demanded a six-year prison term, which would be added to an eight-year sentence Russia's former richest man has been serving since 2003.
He was convicted of tax fraud — a charge that could be levelled against any big businessman in the 1990s.
However, Mr. Khodorkovsky was the only Russian tycoon to be put behind bars in what many thought was a warning then President Vladimir Putin sent to all Russian oligarchs not to meddle in politics.
In the second trial, Mr. Khodorkovsky stands accused of stealing 218 million tonnes of oil worth $27 billion from Yukos, the company he owned before it was taken over by the government in 2004.
Many independent lawyers said the charges were absurd and contradicted the previous court verdict which found Mr. Khodorkovsky guilty of failing to pay taxes for the oil prosecutors now say he stole.
Russia's current and former Economy Ministers who testified in court said they were not aware of any large-scale oil theft in Yukos.
Kremlin critics said the guilty verdict to Mr. Khodorkovsky would be a personal revenge from Mr. Putin, currently Prime Minister, for airing corruption charges and funding opposition parties.
It would also show that President Dmitry Medvedev, who has championed the rule of law and independent judiciary, has little real power in his tandem with Mr. Putin.
