Ukraine's military forces and the Russian-backed rebels they've been fighting since 2014 began withdrawing from the village of Petrivske in the disputed eastern Donbass region on Saturday.
It's one of a series of measures that could pave the way for a peace summit between Russia, Ukraine, Germany and France.
Relations between Kiev and Moscow collapsed after Russia annexed the Crimean peninsula in 2014. That prompted Western sanctions.
Both sides accuse each other of violating a ceasefire that was agreed in the Belarus capital Minsk in 2015.
It's not the first time that the two parties have pulled troops out with the help of the OSCE monitoring mission.
Relations between Ukraine and Russia collapsed following Moscow's annexation of the Crimean peninsula in 2014, which prompted Western sanctions.
Ukraine says after the Crimea annexation Russia engineered quasi-separatist uprisings across a belt of eastern Ukraine that escalated into a full-scale conflict, something Moscow denies.
Two so-called People's Republics, unrecognised by either Kiev or Moscow, have formed in the Donbass region.
According to the UN the fighting in the eastern region has killed more than 13,000 people in five years.