Bulgaria ordered 78 Avia B-534 biplane fighters in 1939. These were obtained from Germany which had captured a large number of them. The final aircraft were not delivered until March 1942. At the same time, Bulgaria ordered more modern fighters such as the Messerschmitt Bf 109E and Dewoitine D.520, which resulted in the outdated B-534s seeing little frontline service. However on 1 August 1943, 48 Avias made several passes at Consolidated B-24 Liberators returning from the raid on Ploieşti. Although several hits were scored, none of the bombers were shot down.

Avia B-534 in Slovak Service

With the partition of Czechoslovalia on 14 March 1939, Slovakia inherited 71 Avia B-534 biplane fighters. Two squadrons participated alongside Luftwaffe units in the invasion of Poland in September 1939. They were later deployed to Ukraine in 1941 during the invasion of the USSR. In 1942, one squadron was returned to Slovakia for anti-partisan operations. By 1943, obsolescence and a lack of spare parts relegated them to training roles.

During the National Slovak Uprising of September-October 1944, a B-534 shot down a Hungarian Junkers Ju 52, the last confirmed aerial victory of a biplane fighter.