This study aimed to investigate the way English Language Teaching (ELT) textbooks portray males and females based on their social roles and subject positions. To this end, Prospect Series, the locally-designed English textbooks currently taught in Iranian high schools, were selected to examine to what extent equality of gender representation has been observed in the series. The study analyzed the series in terms of major gender-related issues: Female and male's characters, pictorial representations, titles, social roles, activities and firstness in mixed-gender dialogues, gender focus of textbook themes/content as well as gender relations. To describe and analyze genders in conversations and pictorial representations, a Critical Discourse Analysis (CDA) approach was applied. Thus, to extract the ideology behind gender representation in the series, Fairclough's (2001) three dimensional model was utilized. The results indicated that the series did not equally display males and females. It was also revealed that only Prospect 2 included sexism. In fact, in this study, a more comprehensive description of textbook evaluation with ideological basis was presented. The findings of the study offer some guidelines to second language (L2) teachers and materials developers to select and design textbooks based on not only the appropriateness of content, but also various other aspects like the textbook characters' social roles and subject positions in terms of gender.