This article analyzes the most frequent modern Lithuanian and Latvian phraseological units with the component ―devil‖, or ―Velnyas‖ in comparison with the Russian language. The study presents several aspects of this issue, in particular, a brief overview of the facts confirming the proximity of these languages to the ancient Indo-European language, and also briefly describes the general ideas of the Balts about Velnyas, which have their roots in the era of paganism, which was preserved among Lithuanians and Latvians until 17th century. The main part of the work is devoted to the analysis of the linguistic material itself, which is divided into three main groups according to the principle of complete matches, partial analogues and non-equivalent units. On the basis of the latter, a conclusion is made about the greater anthropomorphism of the image of the representative of evil spirits among the Balts in comparison with the Russian concept of ―devils‖ due to the rather late adoption of Christianity by the Balts. Taking into account the existence of the Balto-Slavic union in a certain historical period, Lithuanian and Latvian phraseology helps to penetrate deeper into the consciousness of the ancient Slav and restore the picture of his ideas about evil spirits in the pre-Christian period, which were not recorded in written sources, but are confirmed in modern Lithuanian and Latvian phraseology, where these ideas are still preserved.