We examined whether the Protestant work ethic (PWE), a fundamental, individually held belief associated with both sexist attitudes and personal striving, relates to undergraduate female science, technology, engineering, and math (STEM) majors’ perceived identity compatibility (PIC) between being a woman and being in a STEM field and expectations of dropping out of their majors across the beginning of college. Using within-person analyses across six time points, PWE-Equalizer (suggesting hard work is a social equalizer) was positively associated with PIC and inversely associated with expectations of dropping out of one’s major; PWE-Justifier (justifying disadvantage by blaming group members for not working hard enough) showed the opposite pattern. PIC mediated the relationship between PWE and expectations of dropping out. Implications for future directions in research, as well as for educational policy aimed at increasing the numbers of women in STEM fields, are discussed.