Objective To investigate the pharmacodynamics of Mμ-Opioid receptor gene(OPRM1)as a candidate gene to obtain the data on genetic polymorphisms for the study of depression pathogenesis, genetic diagnosis and treatment.Methods Genomic DNA was isolated from the venous blood leukocytes of 393 unrelated patients with depressive disorder and 738 unrelated healthy servicemen.All the polymorphisms were genotyped by PCR-restriction fragment length polymorphisms (PCR-RFLP)and polymerase chain reaction-sequence specific primer(PCR-SSP).Genotypes and allele frequencies were analyzed with SPSS13.0 software and Haploview software.Results There was significant difference in both allele and genotype frequencies of OPRM1 genes between the depressive disorder group and control group(P<0.05).The allele T of rs1799971C/T in the male depressive disorder group aged 34 to 49 was significantly higher than that in the control group(OR=0.564,95%CI:0.196-0.837,P=0.001) The allele A of rs648893G/A was not significantly different between the depressive disorder group and the control group(OR=0.853,95%CI:0.649-1.121,P=0.139).Conclusions OPRM1genes are associated with depressive disorder with exon1 T allele of rs1799971.The OPRM1 gene is susceptible to depressive disorder in northern Han Chinese populations.