Catechol-O-methyltransferase (COMT) is an enzyme that degrades various biogenic amines, which have been hypothesized to be associated with personality traits. We investigated a possible relationship between the COMT Val158Met polymorphism and personality traits assessed by the Temperament and Character Inventory (TCI) in 139 healthy subjects in a Japanese population. The number of Met alleles of the COMT Val/Met genotype tended to relate to harm avoidance (HA) scores parametrically, while no significant difference was observed between genotype groups in either novelty seeking, reward dependence, persistence, self-directedness, cooperativeness or self-transcendence. These results suggest that the Val/Met polymorphism of the COMT gene may play a role in HA in Japanese population.