Lissu, the Chairperson of the main opposition party, Chama cha Demokrasia na Maendeleo (CHADEMA) and runner-up in the 2020 presidential election, was arrested on Wednesday after a rally in the south western region of Ruvuma.
At a court appearance in the commercial Dar es Salaam, Lissu was not allowed to enter a plea on the treason charge. He pleaded not guilty to a separate charge of publishing false information.
The charge will bring fresh scrutiny to President Samia Suluhu Hassan's human rights record, as she bids for re-election.
Hassan won plaudits after coming to power in 2021 for easing repression of political opponents and censorship of the media which proliferated under her predecessor, John Magufuli, who died in office.
But she has faced mounting criticism from human rights activists over a series of arrests and unexplained abductions and killings of political opponents.
Hassan has said the government is committed to respecting human rights and she ordered an investigation into reported abductions last year.
--Reuters--