To analyze the role of mus-genes repair in system activation P-elements in Drosophila melanogaster induced by a chronic exposure to low doses. The materials were dysgenic individuals of Drosophila melanogaster with mutations in repair genes (mus101, mus205, mus304, mus308, mus309) and simultaneous transposition of mobile P-elements. The animals were exposed to a chronic irradiation in low doses (0.42 mGy/h). The reaction of animals was analyzed by the DNA damage rate in somatic cells ('Comet assay'), level of dominant lethal mutations, fecundity, and survival rate. The combined action of the systems of post-replication, recombination repair (mus205, mus304), repair of DNA double-stranded breaks (mus304), and of the transposition activity of P-elements after a chronic irradiation in low doses was identified according to every study parameter. The other repair systems and their genes (mus101, mus308, and mus309) responded to action of only one factor (irradiation or mobile elements transposition). The obtained data significantly contribute to the knowledge on a new reaction of the mechanisms of organisms to a chronic irradiation in low doses.