The proceedings against Zhao Changqing -- a student leader during the 1989 pro-democracy protests in Tiananmen Square -- and Hou Xin are seen as part of a crackdown on the loose-knit New Citizens Movement.
Its members face up to five years in prison for their roles in small-scale protests calling for government officials to disclose their financial assets, seen as a key reform against graft.
The ruling Communist Party says it is conducting its own anti-corruption campaign, but Beijing is extremely wary of any organised dissent against its rule.
Zhao's trial -- which followed that of New Citizens Movement founder Xu Zhiyong yesterday -- opened in Beijing but was halted almost immediately as he sacked his lawyers, one of them, Zhang Xuezhong, told AFP.
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"This dismissal was a tactical choice by the defendant because this was the only way to halt the trial," he said, adding the move gave Zhao 15 days to find a new legal representative.
The activists are all but certain to be convicted by China's politically controlled courts.