AbstractOxytocin represents one of the key element regulating social activity and aggressive behavior via its binding to oxytocin receptor (OXTR). Considering the multifactorial nature of developing aggression, the present study aimed to assess the main effects of the OXTR (rs53576, rs237911, rs7632287, rs2254298, rs2228485, rs13316193) gene polymorphisms together with haplotypic and G × E effects on individual differences in aggression level in 623 mentally healthy individuals with sex and ethnicity as covariates. The association of rs2228485*G allele (PFDR = 0.046) and rs237911*G allele (PFDR = 0.046) and decreased aggression level was observed in Tatars. Haplotypic analysis revealed an association of the OXTR G*G*G haplotype (rs53576, rs2228485, and rs237911) and diminished aggression level (Pperm = 0.020) in Tatars. As a result of multiple regression analysis, we observed the modulating effect of smoking and paternal overprotection significantly affecting association of the OXTR rs2228485 and aggression level (P = 0.029 and P = 0.014, respectively) in the total sample.