The trial of Alaa Abdel-Fattah and 24 other activists began in Cairo on Sunday.
They are charged with offences related to a protest against military trials of civilians outside the Shura Council in November 2013.
It was one of the first protests dispersed by force in accordance with a controversial new protest law, which criminalises unauthorised demonstrations.
The No to Military Trials campaign group claimed responsibility for organising the protest, but Abdel-Fattah was charged with being its instigator.
Abdel-Fattah was also charged with assaulting members of the security forces and stealing an officer's walkie-talkie.
He was arrested at his home on 28 November 2013 and has been detained for over 110 days in what activists say is an illegal detention.
No to Military Trials activist Ahmed Abdel-Rahman has been detained for over 100 days on similar charges. He was arrested during the dispersal of the protest.
The trial date was set two weeks ago after activists protested at the prosecutor-general's office to complain the detainees were being held without trial.
During his detention in Tora prison, Abdel-Fattah has published four letters about the revolution and his fellow detainees.