Those released on Thursday include soldiers who defended the Azovstal steel plant, Ukraine said.
Russia and Ukraine have swapped 50 service personnel in the latest prisoner exchange between the two sides since the war began.
A Russian-installed official in Ukraine's Donetsk region confirmed on Thursday that Moscow and Kyiv would each hand over 50 prisoners of war.
Andriy Yermak, the head of Ukraine's presidential administration, later stated that 50 "protectors of Ukraine" had been released.
"The defenders of Mariupol and Azovstal have returned, also those captured ... in the battles in the Donetsk, Luhansk, and Zaporizhzhia regions," Yermak wrote on Telegram.
He added that the exchange of prisoners would continue until the "last Ukrainian" had been freed.
Moscow said it would fly the released Russian prisoners to the capital for medical checks and rehabilitation.
Russia and Ukraine had each exchanged over 50 prisoners of war exactly one week ago, according to a report by Reuters.
Representatives from each country were said to have met in the United Arab Emirates last week to discuss the swap, with involvement from the United Nations.
Neither Russia nor Ukraine have released official figures on how many prisoners of war they have taken since the invasion began exactly nine months ago.
Ukraine's president Volodymyr Zelenskyy said on Thursday that Russia had freed 1,319 prisoners since March.
“We will not stop until we get all our people back,” Zelenskyy wrote on Instagram.