"Syrian authorities on Tuesday freed Maria Bahjar Shaabo without charges," human rights lawyer Anwar Bunni told AFP.
Maria is the daughter of two anti-regime activists and was born in jail in 1988 while her mother was serving a four-year sentence for political activism.
She was a year-and-a-half old when her father was able to get her out of jail. He cared for her until her mother's release, only to then be jailed himself for some 10 years.
Prior to her arrest, Shaabo had travelled to Lebanon to visit her mother, who was participating in a medical conference.
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She was arrested on November 2 by Syrian intelligence services just after crossing the border on returning from Lebanon.
Bunni told AFP that two activists, Omar al-Shaar and Jadia Nawfal, who were arrested with Shaabo, are still being held.
Rights groups including Amnesty International have called for Shaar and Nawfal's release.
Around 200,000 people are being held in Syrian jails on political charges, and rights groups say they fear for their lives.