Instructional materials are one of the areas in which gender inequality is very easily institutionalised. The study investigated gender representation in high school English textbooks in Afghanistan. High school English textbooks were used as the corpus of the study. A mixed content analysis approach was used to analyse the data. The frequency of items for each category was counted and tabulated. The findings showed that women were substantially underrepresented whereas men were significantly overrepresented in text and illustrations. Male characters were placed before female characters in all coordinated phrases, and none of the dialogues was initiated by female characters. Women were portrayed in a limited number of social roles while men occupied a wide range of them. Moreover, masculine generic forms were widely used to refer to both women and men. Thus, it is concluded that high school English textbooks promote and perpetuate gender inequality in Afghanistan.