This study was designed to investigate the relationship between self–concept and students’ achievement in Mathematics and to find out the predictive strength of self–concept on academic achievement among secondary school students. The sample consisted of 205 girls and 245 boys randomly selected from four girls’ schools and four boys’ schools in Ekiti State. In order to determine the degree of relationship between students’ achievement in Mathematics and self concept, stepwise multiple regression analyses was computed at 0.05 significant levels. The results of the study show that there is a significant relationship between self–concept and Mathematics achievement of secondary school students and that Mathematics achievement could be predicted moderately by self–concept measures. This study seems to have created yet another conflict of result with the common view that self concept and achievement patterns of individuals may be positively and highly correlated. Hence, there is need for counselling programmes both at individual and group level focusing on enhancing emotional and social comfort and the holistic self–concept of college students.