Joakim Medin, a 30-year-old freelance reporter, told the Expressen newspaper that he was seized at a road block along with his Kurdish interpreter Sabri Omar while working in the Kurdish town of Qamishli on the border with Turkey.
Both were reportedly freed late Saturday night.
"I was taken by the regime," Medin told the newspaper.
Swedish Foreign Ministry Spokeswoman Ulla Jacobson confirmed Medin's release but could not provide further details.
"He is free, we have been in touch with him," she told AFP.
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Medin told Expressen he was not subjected to violence but was interrogated and held in solitary confinement in a tiny cold dark cell "full of dirt and blood".
"I was there to report on the situation and hadn't entered the country the official way via the Syrian government," he said, adding that Syrian soldiers questioned him about his links to the Kurds, Turkey and Israel.
Medin has worked for Swedish media in Kurdish areas of Syria since 2014, including the border town of Kobane which was over-run by militants from the Islamic State group and liberated by Kurdish forces last month after more than four months of fighting.
In December he was arrested by Turkish border guards and interrogated for illegally entering the country from Kobane.
According to Expressen, a Kurdish group -- the Democratic Union Party (PYD) -- negotiated for the release of the Swede and his interpreter with Syrian forces in return for Syrian soldiers captured by Kurdish fighters.