Outside the court, riot police were out in force.
Hundreds of supporters of Tymoshenko gathered outside the courthouse in the centre of Kiev, and there were scuffles.
People also demonstrated against the ex prime minister, raising fears of unrest.
At one point police cleared a blocked road, detaining several people.
One woman told euronews: “Yulia Tymoshenko is in jail for political reasons, it’s political repression. We came here to defend Yulia Tymoshenko, to defend freedom. We’re ready for the revolution, with our blood as well.”
A man said: “12 million people voted for Yulia Tymoshenko and they are here today. There is an action plan to defend Yulia Tymoshenko all over Ukraine.”
The US and the European Union say they believe the trial is politically motivated and have called for her release.
The case comes at a time when Ukraine is attempting to improve its ties with the West, and Kiev is being warned that economic agreements are at risk.