Several hundred supporters of the nationalist party Vazrazhdane or Revival protested against sending military aid in front of the parliament.
Bulgaria is sending protective equipment to Ukraine for the first time, but no weapons.
The government of the EU and NATO members decided to support Ukraine with 2,000 helmets and 2,000 protective vests.
They were to be used by the civilian population, cabinet spokesperson Lena Borislavova said.
The governing coalition in Bulgaria consists of four parties unable to agree on the issue of arms deliveries to Ukraine.
Several hundred supporters of the nationalist party Vazrazhdane or Revival protested against sending military aid in front of the parliament and the seat of government in Sofia.
They also rejected a possible stationing of NATO soldiers and equipment in the south-eastern European country.
“This way, we will make ourselves accomplices and give cause for a war on our territory as well as for retaliation,” one demonstrator said.
The co-ruling Bulgarian Socialist Party, the successor to the Communist Party, also opposed military support for Kyiv, as their voters were usually friendly toward Russia.
(dpa/NAN)