A court on Monday dismissed one case against Tunisian Femen activist Amina Sboui in which she was tried for contempt and defamation, her lawyer said, calling the verdict "a victory".
But Ghazi Mrabet said Sboui still faces a pepper spray charge which carries a prison sentence of between six months and five years.
She could also be charged with desecrating a cemetery for which she could be jailed for up to two years if found guilty.
"The court decided to dismiss the case against Amina. It is a victory, the judiciary has begun to understand that she has been unfairly prosecuted," the defence lawyer said of the contempt and defamation charge.
She was on trial on those two counts after she charged that detainees were tortured in the prison where she has been held since May after daubing the word "Femen" on a wall near a cemetery in the city of Kairouan.
She was protesting against an annual congress that hardline Salafists had planned to hold in the historic Islamic centre of learning before the government banned it.
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Amina's mother said the verdict was "reassuring".
"I am happy with this decision, it is reassuring for what comes next.I have faith against in the judicial system," she told AFP.
Amina had sparked both scandal and a wave of online support after she was threatened by Tunisia's increasingly active hardline Islamists for posting topless pictures of herself on Facebook earlier this year.
Her family said that she suffered from chronic depression and had suicidal tendencies, and they prevented her from going out, claiming her safety was at risk.
But the young woman, who accused her relatives of holding her in captivity and beating her, ran away from home in April and had regularly appeared in public before her detention in May, although never topless.
The Femen movement, founded in Ukraine and now based in Paris, has flourished since 2010, with feminists around the world stripping off in protest at a wide range of issues linked to the mistreatment of women, but also against dictatorship.
At the end of May three Femen activist, two French and a German, were arrested after bearing their breasts outside the main Tunis courthouse, in a demonstration of support for Amina.
The arrest of the three women triggered international condemnation and they were later released.