"I call for an international tribunal to be set up which would investigate the crimes of Lukashenko's dictatorship in the past and during the election in 2020," Tsikhanouskaya, who is now based in Lithuania, told the Czech Senate.
Tsikhanouskaya, who met Czech president Milos Zeman and prime minister Andrej Babis during her visit to the Czech Republic, gave no other details of her proposal.
She said the only solution to the situation in Belarus was holding free elections with international monitors.
Tsikhanouskaya was visiting Prague before a summit of the Group of Seven advanced economies in Britain this week at which Belarus is expected to be discussed.
The former Soviet republic outraged Western countries last month by ordering a Ryanair flight to land in the capital Minsk and arresting a dissident journalist who was on board.
Lukashenko has dismissed Western criticism over the incident, and accused Western countries of waging a ‘hybrid war’ against him.
The United States and the European Union are preparing to tighten sanctions on Belarus over the plane incident.