Police detained several demonstrators trying to attract attention to their own causes, escorting a elderly woman wearing a paper hat labelled "Injustice" away from the court in Jinan.
"I want to see if China's courts are fair or not. Are they only unfair to people like us or to everyone?" said another woman, Lin Xiuli, 43.
Lin said she had applied to attend Bo's trial, and came to see "what the difference is between cases for top officials and for us regular people".
Attendance at the proceedings -- which analysts say are meant to bring to a close a scandal which exposed deep divisions and corruption at the highest levels of the Communist Party -- is likely to be strictly controlled, with independent media barred from entry.
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The protester detentions occured in front of a gaggle of reporters -- kept away from the courthouse by a cordon -- while more demonstrators arrived later.
Several identified themselves as petitioners -- citizens with decades of personal grievances who file complaints with more senior departments, but often face illegal detention.
She and four other protesters had a noisy row with police, while another group who said they travelled to the courthouse from China's commercial hub Shanghai hurriedly handed papers to journalists and called out as police ushered them away.
The extremely sensitive trial has been anticipated for around a year and a half, since Bo was dismissed from his position as head of the megacity of Chongqing and as a member of the ruling Communist Party's 25-strong Politburo.
About 50 police practised drills in the morning on the grounds of the courthouse, a broad and stately structure with a Chinese flag at its entrance. They worked with sniffer dogs and a few wore bullet-proof vests.