The present correlational study sought to determine the mediating role of academic motivation in the relationship between attachment to mother and academic performance among 303 Tehrani eleventh graders majoring in natural sciences (134 boys and 169 girls). The participants completed the Academic Motivation Scale (AMS) (Vallerand & Bissonnette, 1992) as well as the Inventory of Parent and Peers Attachment (IPPA) (Armsden & Greenberg, 1987). In addition, the students’ academic performance was estimated through their average scores on physics, chemistry and biology final examinations. The validity and reliability of the instrumentation were obtained by confirmatory factor analysis and Cronbach's alpha coefficient. The data were analyzed using structural equation modeling. Results were indicative of the goodness of fit of the model and showed that attachment to mother and academic motivation accounted for 33 percent of the variance of academic performance. Furthermore, attachment to mother predicted 36% of the variance of academic motivation. It can be concluded that attachment to mother affects adolescents’ academic motivation and thus improves their academic performance.