The exchange was the result of direct talks between the two sides in Istanbul on June 2 that resulted in an agreement to exchange at least 1200 POWs on each side and to repatriate thousands of bodies of those killed in Russia's war in Ukraine.
The return of POWs and the repatriation of the bodies of the dead is one of the few things the two sides have managed to agree on as broader negotiations have failed to get close to ending the war, now in its fourth year.
Fighting has raged on, with Russia saying on Monday its forces had taken control of more territory in Ukraine's east-central region of Dnipropetrovsk and Ukraine saying Russia had launched its largest drone attack of the war.
Officials in Kyiv said some of the Ukrainian prisoners who came home on Monday had been in Russian captivity since the beginning of the war.
At a rendezvous point for the returning Ukrainian prisoners, soon after they crossed back into northern Ukraine, an official handed one of the freed men a mobile phone so that he could call his mother, a video released by Ukrainian authorities showed.
"Hi mum, I've arrived, I'm home!" the soldier shouted into the receiver, struggling to catch his breath because he was overcome by emotion.
The released Ukrainian men were later taken by bus to a hospital in northern Ukraine where they were to have medical checks and be given showers, food and care packages including mobile phones and shoes.
Jubilation was tinged with sadness because outside the hospital were crowds of people, mostly women, looking for relatives who went missing while fighting for Ukraine.
The women held up pictures of the missing men in the hope that one of the returning POWs would recognise them and share details about what happened to them.
Some hoped their loved ones would be among those released.
Oksana Kupriyenko, 52, was holding up an image of her son, Denys, who went missing in September 2024.
"Tomorrow is my birthday and I was hoping God will give me a gift and return my son to me," she said, through tears.
Neither side said how many prisoners had been swapped on Monday but the Russian Defence Ministry said in its own statement that the same number of military personnel had been exchanged on each side.
Ukrainian President Volodymyr Zelenskiy, speaking in his nightly video address, said the exchanges would be conducted over several stages.
"The exchange process is expected to take more than a single day. The details of the process are quite sensitive," he said.
"That's why there is currently less information than usual."
Zelenskiy also said Ukrainian forces were engaged in heavy fighting near Pokrovsk in the east and inside Russia's Kursk region and also in Ukraine's Sumy region, where Russian forces are trying to establish a presence in several border villages.
Kremlin aide Vladimir Medinsky said at the weekend that a first list of 640 POWs had been handed to Ukraine.
The Russian military said its returned servicemen were now in Belarus, where they were receiving psychological and medical assistance before being transferred to Russia for further care.
Footage broadcast by Russia's RIA state news agency showed a group of freed Russian soldiers on board a coach raising their hands in the air and shouting: "Hurrah we're home."
"It is very difficult to convey what I'm feeling inside now. But I am very happy, proud and grateful to everyone who took part in this process, in the exchange and bringing us home," one freed Russian soldier said.
Both sides say the intention for this round of prisoner swaps is also to hand over people who are gravely ill or severely injured.
The people seen being handed over so far on Monday appeared to be fit and well.
