HIV/AIDS continues to pose challenges to the health system of developing countries. Substance use has been identified as an important behavioral co-factor for HIV infection. Aim: To evaluate the knowledge and effectiveness of HIV educational programme in Patients with Substance Use Disorders (PSUD). The study was carried out among 30 in-patients with substance use disorder at the Center for Addiction Medicine and male open psychiatric wards in a south Indian psychiatric hospital. A non equivalent control group pretest post test design was adopted. Convenience sampling method was used to recruit the study subjects. Results: The analysis showed that mean pre-intervention knowledge of the experimental and control groups were 20.53 ± 5.67 and 20.53 ± 4.53 respectively indicating that both groups were homogenous. The experimental group showed higher immediate post test and follow up test mean knowledge scores on the Knowledge Questionnaire on HIV prevention (KQ-HIVP) (p=0.001) as compared to the scores of the control group following the education program on HIV prevention. Conclusion: Educating and demonstrating protective measures such as precise use of condom and safe use of injections are the prime areas to be addressed in a HIV education program. This educational program should be integrated with other psychosocial therapies to cater to holistic needs of patients receiving treatment at centers’ for addiction medicine.