Dopamine and norepinephrine are implicated in the characterization of personality traits. Dopamine-beta-hydroxylase (DBH) is the enzyme responsible for conversion of dopamine to norepinephrine, and thus plays an important role in controlling dispositions of these neurotransmitters. Previous studies have shown that the -1021C/T polymorphism of the DBH gene promoter influences plasma DBH activity. Therefore, we examined the association between the -1021C/T DBH polymorphism and personality traits in 627 Japanese healthy volunteers. The DBH genotypes were identified by a PCR-RFLP method, and personality traits were assessed by the Temperament and Character Inventory (TCI). In the two-factor analysis of covariance with the DBH genotype and sex as factors and with age as a covariate, there was no main effect of the DBH genotype on any TCI score, while the interaction between the factors was significant in harm avoidance. In the post hoc analysis, the group with the T allele predictive of lower DBH activity had higher scores of harm avoidance than that without the T allele in females (p=0.006), but not in males. The present study suggests that the -1021C/T DBH polymorphism affects the personality trait of harm avoidance in healthy females.