The move on Sunday was part of an agreement made earlier this month at a summit between Ukraine, Russia, Germany and France.
Some 142 prisoners are expected to be swapped at a checkpoint near Horlivka in eastern Ukraine.
Ukraine is to release 87 people and the rebels will send 55.
The last major prisoner swap between the two sides took place in December 2017. The rebels exchanged 73 Ukrainians for 233 of their own.
More than 14,000 people have been killed in the region since 2014.
The conflict began about two months after Ukraine’s pro-Russia president Viktor Yanukovych fled the country as massive protests broke out in Kiev.
Russia’s annexation of the Crimean Peninsula happened shortly after.