The presence of a complex structured brain, the anterior department of which (telencephalon) has no analogues in other groups of animals, is a significant peculiarity of vertebrates (including the human). Previously, a vertebrate-specific monogenic class of homeobox genes Anf, which plays a key role in the development of telencephalon, was discovered in the Laboratory of Molecular Bases of Embryogenesis (Institute of Bioorganic Chemistry, Russian Academy of Sciences). Out of all vertebrates, the Anf genes were not found only in the members of the most ancient group of jawless fishes (modern lampreys and hagfish), while the telencephalon was described in these animals. According to the literature data, a branch leading to jawless fishes separated from common vertebrate stem at the earliest stages of the their evolution, and detection of the Anf genes in jawless fishes is important, since it could confirm the previous hypothesis that the origin of telencephalon in evolution was associated with the appearance of the homeobox Anf gene. In the present work, the Anf gene was for the first time described in the Pacific lamprey (Lethenteron camtschaticum), the pattern and dynamics of its expression were studied at early stages of the development of this lamprey species, and the translation of its full-size cDNA was conducted in a eukaryotic expression system (clawed frog embryos).