We investigated the effect of differential perceived efficacy to reduce racial inequality (in the context of increased awareness of illegitimate in-group advantages) on White Americans' intergroup attitudes and antidiscrimination behavior. White American university students read a passage describing the underrepresentation of African Americans in their university's faculty and then wrote letters to the university administration in support of appointing more African Americans to the faculty. We experimentally varied feedback concerning efficacy to change institutional racism. Before writing their letters, participants were told that there was a low, moderate, or high chance that their efforts would be effective. Later in the experiment, participants' perceived efficacy to influence their university system was measured. Intergroup attitudes improved and antidiscrimination actions increased among participants with higher perceived efficacy in comparison with participants with low perceived efficacy. Collective guilt partially mediated the effects of efficacy beliefs on antidiscrimination actions and fully mediated the effects of efficacy beliefs on intergroup attitudes.