We investigated the reliability of the HEXACO‐Personality Inventory (HEXACO‐PI) using the NEO Five‐Factor Inventory (NEO‐FFI) and the International Personality Item Pool (IPIP) Big Five scales in a Japanese sample of 492 respondents (mean age = 20.4 years). The psychometric properties of the HEXACO‐PI were examined and found to be satisfactory. The results of the factor analysis showed that the six hypothesized personality domains were found independently. A total of 307 participants responded to the NEO‐FFI and the IPIP Big Five scales. The results showed that the five domains of the HEXACO model corresponded to the Five‐Factor domains and were relative to the Big Five personality domains as a whole, but the sixth domain, Honesty‐Humility, showed weak to moderate correlations with some factors of the NEO‐FFI and the IPIP Big Five scales. These results suggest that the Honesty‐Humility domain is independent of the five fundamental personality factors and that the HEXACO‐PI is a useful and reliable questionnaire for investigating personality structure in cross‐cultural and other context.