Background/aim: The aim of the study was to analyze the relationship of the immune response mediator genes' polymorphic loci (TNFA rs1800629, LTA rs909253, IL1B rs16944, IL2-IL21 rs6822844, IL2RA rs2104286, IL6 rs1800795, IL10 rs1800872, MIF rs755622, CTLA4 rs3087243, NFKB1 rs28362491, PTPN22 rs2476601, PADI4 rs2240336) variants with the methotrexate efficacy in juvenile idiopathic arthritis (JIA). Materials and methods: The study included 274 JIA patients from the Republic of Bashkortostan, Russia. Achieving the American College of Rheumatology Pediatric 30 (ACR Pedi 30) response was regarded as the presence of the response to methotrexate (otherwise, as the absence), while achieving clinical remission on medication (Wallace et al., 2011)-as the sufficient response (otherwise, as the insufficient). Genotyping was conducted by the real-time polymerase chain reaction. Results: Associations with an altered risk of the nonresponse to methotrexate in JIA were observed for the alleles/genotypes of the loci IL10 rs1800872 (in girls) and NFKB1 rs28362491 (in girls); with an altered risk of the insufficient response to methotrexate in JIA – for the alleles/genotypes of the loci IL1B rs16944 (in boys), CTLA4 rs3087243 (in boys), NFKB1 rs28362491 (in girls) and the haplotype TNFA rs1800629*A-LTA rs909253*G (in girls). Conclusion: As a result of the study, the relationship of the alleles/genotypes of the IL1B rs16944, IL10 rs1800872, CTLA4 rs3087243, NFKB1 rs28362491 polymorphic loci and the TNFA rs1800629*A-LTA rs909253*G haplotype with the methotrexate efficacy in JIA was established (taking into account the differences by sex).