The protesters gathered to oppose Bill No.13646, which addresses the legal status of missing persons.
Participants said that certain provisions of the legislation could allow courts to declare missing Ukrainian military personnel legally dead before their fate has been confirmed.
"Today all the families came out so that the missing are not equated with the dead," said Mariana Yatselenko, 27, who took part in the Kyiv march.
More than 90,000 people are listed as missing in Ukraine's unified registry of persons who disappeared under special circumstances, according to Artur Dobrosierdov, the country's commissioner for missing persons.
Neither Russia nor Ukraine publish regular casualty numbers in the war, although analysts estimate hundreds of thousands of casualties in the fighting.
The Ukrainian register covers people who went missing during combat as a result of armed aggression or in occupied territories, mostly after Russia's all-out invasion began on February 24, 2022.
But some cases date back to 2014, when Russian soldiers invaded the Crimean Peninsula and pro-Russia forces started fighting in eastern Ukraine.
The registry began operating in May 2023, and at that point, information about both military personnel and civilians from previous years was entered into it.
Similar demonstrations have been held previously over the bill, reflecting growing pressure from relatives of soldiers who are missing.
