The study aims at finding out the Self-Efficacy and Achievement Motivation among higher secondary school students based on Gender and Medium of instruction. The sample taken for the study is about 1200 higher secondary school students of Chennai and Ponneri Educational Districts who had opted Biology as one of the subject of study. The Achievement Motivation Inventory was developed by Muthee J.M & Immanuel Thomas (2009) and General Self-Efficacy Scale developed in Germany by Mathias Jerusalem and Ralf Schwarzer (1979), was used and created as a survey instrument by Big Brothers Big Sisters (BBBS) of greater Rochester was used in the study. The major findings of the study indicate that there is a significant difference in the Self-Efficacy and Achievement Motivation based on Gender and Medium of Instruction among higher secondary school students and also Girls exhibit higher Self-Efficacy and Achievement Motivation than that of Boys. There also exists significant relationship between Self-Efficacy and Achievement Motivation among adolescents.