Abstract: Objective To explore the relationship between single nucleotide polymorphism(SPN)of a novel tryptophan hydroxylase isoform(TPH2)gene rs4570625 and depression and suicidal behavior. Methods We collected the specimens of peripheral blood from 300 uniplor depression patients and 300 healthy controls in a mental hospital in Harbin city.The amplification of novel tryptophan hydroxylase isoform(TPH2)gene rs4570625 was executed by polymerase chain reaction(PCR)and analyzed with direct sequencing.The association between the polymorphisms of TPH2 gene and depression and suicidal behavior was analyzed with SPSS 11.0. Results The genotypic frequencies of the SNP didn't deviate from Hardy-Weinberg equilibrium in both case and control groups(P>0.05).Compared with the control group, no significant difference in genotypes and alleles of TPH2 gene rs4570625 was found in the patient group(P>0.05). Meanw hile there was no significant correlation between genotypes of TPH2 gene rs4570625 and suicide behavior in patient group.There were significant differences in T,G frequencies of TPH2 gene rs4570625 between the patients with and without suicidal behavior(56.5% vs 47.6%,43.5% vs 52.4%;P<0.05 for all). Conclusion TPH2 gene rs4570625 SNP may have no association with the susceptibility of depression.