Adolescence is the second decade of life (13-19 years), and a period of both physical as well as psychological development. This is a phase of experimentation and risk that includes early sexual debut, sexual coercion and violence, trafficking, and substance abuse. Along with these, other factors such as the lack of knowledge about HIV/AIDS, inaccessibility to health care services and commodities, lack of education and life skills, and early marriage have increased their vulnerability to HIV/AIDS. Since adolescents comprise a major part of reproductive group, they are likely to play a significant role in determining the future growth pattern of India’s population and economy. Thus, it is crucial that investment in terms of finances, research and development policies be done to improve their well-being. A pre-experimental one group pre-test, post-test research design was selected for this study to gather data from adolescents regarding prevention of AIDS. A sample of 100 adolescents was selected using purposive sampling technique. Structured questionnaire was used by the investigator for data collection. Video-assisted teaching was administered to adolescents to improve their knowledge. The structured knowledge questionnaire and video film (video-assisted teaching material) were validated by the experts. Further, pilot study was conducted on 10 samples to assess the reliability of the questionnaire where Karl Pearson correlation co-efficient (r=0.86) proved the reliability. After the pilot study, main study was carried out on 100 adolescents. As a first step pre-test knowledge of adolescents was assessed. Thereafter, video-assisted teaching was provided to the same sample. The same teaching materials were also provided in CD form. Finally, post-test knowledge was taken after 7 days with the same sample. Opinion regarding video film was also taken on day 7. This study revealed that there is significant difference between mean pre-interventional and post-interventional knowledge score on preventive measures of HIV / AIDS among adolescents (mean difference=2.0 and t-value=21.51, significance at 0.05 level). On the basis of its hypothesis H1 was accepted. It signifies that video-assisted teaching is effective in increasing the knowledge of adolescents.