The study aimed to investigate the relation between patriarchal family environment and zero-sum beliefs, and the mediating effect of sexism on the relation based on the Instrumental Model of Group Conflict (Esses et al., 1998). This study also examined the moderating effect of gender on the relation between patriarchal family environment and sexism, and the moderated mediating effect of gender through sexism. Participants were 310 first-year college students (234 males and 76 females) in the college of science and engineering, and they completed a survey consisting of patriarchal family environment, sexism, and zero-sum belief. Data were analyzed using SPSS Macro Process, and the results indicated that the relation between patriarchal family environment and zero-sum beliefs was fully mediated by sexism. In addition, the relation between patriarchal family environment and sexism was moderated by gender. Specifically, patriarchal family environment significantly predicted sexism for men, but not for women. Moreover, only for men, sexism mediated the relation between patriarchal family environment and zero-sum beliefs. Therefore, patriarchal family environment could cause sexism which could promote zero-sum beliefs for men.