Genetic factors and environmental influences contribute to the determination of human personality traits. This study examined the influence of serotonin receptor 2A polymorphisms and parental rearing on temperament. Subjects included 1245 Japanese volunteers (592 males and 653 females). Three single-nucleotide polymorphisms (SNPs) (rs6311, rs6313 and rs643627) were selected for genotyping. All subjects completed the 125-item Japanese short version of the temperament and character inventory, and 572 completed the Japanese version of the Parental Bonding Instrument. All SNPs were in Hardy-Weinberg equilibrium. A significant association (P=0.0026) was observed between rs643627 and novelty seeking in females. On the other hand, significant effects of maternal overprotection to harm avoidance (HA) were seen for rs6311 (P=0.0005), rs6313 (P=0.0004) and rs643627 (P=0.0003) in males only. In terms of the interaction of genotype and maternal overprotection with HA, interaction was observed in rs6311 (P=0.0290) and rs6313 (P=0.0230) in females only. Our results indicate a relationship between the rs643627 polymorphism and novelty seeking in females. In terms of serotonin receptor 2A gene polymorphisms and maternal overprotection, our findings suggest the existence of a gene-environmental interaction that influences HA.