Based on Kray et al.’s (2017) Study 4, we conducted two studies investigating the relationships between implicit gender role theories (i.e., people’s belief about the fixedness versus malleability of gender roles) and gender system justification using two Japanese samples. As predicted, we found that, for women and men, implicit gender role theories positively correlate with system justification; individuals with a strong belief in the permanence of gender roles supported the status quo in social relations between men and women (Study 1 and 2). However, contrary to our predictions, we found no significant mediating effect of male gender identity on the relationship between implicit gender role theories and system justification (Study 1). Nor did we find a significant moderating effect of zero-sum beliefs on the relationship between male gender identity and system justification (Study 2). Results are discussed in relation to the large gender gap in Japan.