Empathy is sharing and understanding others' emotions. Recently, researchers identified larger Western–Asian cultural differences in self-report empathy with females relative to males (i.e., the culture–sex interaction theory). Neglecting this phenomenon, previous researchers focused on identifying the cultural impact on empathy per se and reported divergent results. This meta-analysis aims to reveal the heterogeneity of the earlier publications and decode the heterogeneity as per the culture–sex interaction. The current results suggested the following: First, the cultural impact on empathy increased along with three sex stratification categories (male-only, mixed-sex, and female-only, in that order). Second, the effect size statistically differed between the binary classifications of sex (female-only > male-only). Third, the mixed-sex samples' effect size was positively regressed on the samples' sex ratio (i.e., percentage of females). The current results revealed the heterogeneity of previous publications and highlighted the significance of the culture–sex interaction effect on empathy for future investigations.