Former Ukrainian PM Yulia Tymoshenko has been jailed for seven years.
A judge ruled she had criminally exceeded her powers when she signed a gas deal with Russia in 2009.
Mrs Tymoshenko said the charges against her were politically motivated. She vowed to appeal against her sentence and fight for Ukraine "till her last breath".
The US and the EU have condemned the charges as selective prosecution of political opponents.
European officials suggested that jailing Mrs Tymoshenko would be a serious blow to the country's hopes of integration with the European Union.
Riot police stood outside the court as thousands of supporters and opponents gathered. There have been minor clashes and some arrests.
Judge Rodion Kireyev said the former prime minister would also have to pay back 1.5bn hrivnas ($186m) lost by the state gas company as a result of the deal.
BBC News - Ukraine ex-PM Yulia Tymoshenko jailed over gas deal