Ukrainian President Volodymyr Zelenskyy said his troops would return with more weapons to fight Russia in the east of the country.
"We will return thanks to our tactics, thanks to the increase in the supply of modern weapons," Zelenskyy said.
Ukraine doesn't give up.
Russia said on Sunday that it had taken the city, which means it now has every city in Luhansk. On the same day, the Ukrainian armed forces confirmed their withdrawal.
Zelenskyy said that the Ukrainian troops left Lysychansk because they were moving away from areas with the most weapons.
He said that Ukrainian troops could fight there with more weapons.
He didn't say where the weapons would come from or what they would be used for.
Some of their losses could be prevented if those countries had supplied more weapons.
The UK's Ministry of Defence said on Monday that Russia's takeover of the Luhansk region means it will focus on taking the other eastern Ukrainian region.
Russia has positioned itself in the Donbas area because it failed to take the whole country quickly in its invasion. Thousands of people have died as a result of the fighting between Russia and Ukraine.
Zelenskyy and other Ukrainian officials have made it clear that they will not give up any land to Russia.