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.