Flaviviruses are subdivided into three groups— mosquito-borne, tick-borne and no-known vector viruses. Tick-borne encephalitis virus (TBEV) is the most widely spread flavivirus in Eurasia which is transmitted to man by tick bytes and causes severe neuroinfection with lethal outcomes. Ticks are main carriers and reservoir hosts of the TBEV in nature. Their ability to feed on a variety of vertebrate animals, intracellular digestion of blood, their long life cycle up to 3-6 years at each stage of development and transovarial transmission of the TBEV make them ideal vectors. Natural TBEV infection had been revealed for 16 species of ixodid ticks. Methods: TBEV strains were isolated from a pool of mosquito Aedes vexans and ticks Ixodes persulcatus Schulze in new-born mice and porcine embryo kidney cells. Nucleotide sequences of reverse` transcription-PCR products were determined using DNA analyzer ABI 3500 (Applied Biosystems, USA). Assembling of the nucleotide sequences into complete genomes of the TBEV strains, their alignment and phylogenetic analysis were performed using MEGA 6.06.