Previous research has shown that people's gender identification correlates with their social dominance orientation (SDO). A question is whether gender identification mediates or moderates the effect of biological sex on SDO. We examined the correlations of sex and gender identification with SDO using the Bem Sex Role Inventory in Study 1 and a gender diagnostic measure in Study 2. Both studies showed that gender identification was significantly associated with SDO. In Study 1, gender identification partially mediated the effect of sex on SDO; and in Study 2, this mediation was complete. There were no indications that gender identification moderated the effect of sex on SDO. The results are discussed against the background of the gender invariance hypothesis of SDO.