In this paper, we integrate three bodies of literature on higher education—horizontal stratification, diversified college expansion, and gender segregation—to generate new insights into the consequences of diversified higher education for gender segregation and inequality. We specifically examine the case of Japan, where college expansion and women’s increasing enrollment in four-year universities have been driven by the proliferation of nonselective private sectors. Two sets of analyses using administrative and survey data reveal the following findings. First, the relative increase in female enrollments in private institutions is driven by the growth of vocationally oriented programs, which typically offer publicly certified licenses for femaledominant occupations. If there was no such increase, then gender segregation in terms of fields of study would have decreased more than observed. Second, we find that those from low socioeconomic background are more likely to be enrolled in vocational fields such as nursing, education and home economics. These results suggest that women’s increased college attendance in Japan contributes to the growth of double gender segregation in terms of fields of study and institutional selectivity by incorporating less privileged women into these sectors.