The purpose of this study was to examine the associations between the Big Five personality traits and a person’s body mass index (BMI). We used three large datasets (survey 1, N = 3,063; survey 2, N = 4,242; survey 3, N = 17,471) including Japanese participants and examined the associations using correlation and multiple regression analyses. Consecutively, we conducted a meta-analysis including the results in the present study and a previous study. The results of these analyses show that Conscientiousness is consistently negatively associated with BMI. Extraversion is positively associated with BMI only for male participants. The pattern of relationships between the Big Five personality traits and BMI in Japan is similar to Western countries rather than to other East Asian countries. We discuss these associations in terms of eating habits and lifestyles.