At the level of secondary school, student's self-concept about their academic capabilities plays an important role. The aims of the study were to examine the relationship between academic self-concept and academic achievement of secondary students and to compare the academic self-concept of male and female secondary students. Sample of the study were 615 secondary school students of both genders (Male 317, Female 298, aged 14-17 years). The sample was drawn from 15 secondary schools affiliated with CBSE board, session 2016-17 of Varanasi city, India. Academic achievement was measured by self-reported Cumulative Grade Point Average (CGPA) of the previous year. Academic self-concept was measured using Kample and Naik (2013) Academic Self Concept Scale (ASCS), which was composed of 57 items, distributed in 8 subscales namely Academic Ability, Academic Interests, Study, Examination, Academic Interaction, Academic Efforts, Curriculum, and Academic Future. The result of the study revealed that there was a positive relationship between academic self-concept and academic achievement and this relationship was stronger for female students (r = .28) than that of male students (r = .17). Moreover, gender differences in the academic self-concept of the students were also found. Female students had significantly higher academic self-concept than male students.