A secondary analysis of 250 HIV-positive drug users who wereenrolled in Methadone Maintenance Therapy (MMT) program in Ho Chi Minh city. Using Generalized Estimating Equations statistical models to determine factors associated with drug use during two years of treatment. The results showed that some significance related fators include: patients had IDU sex partners, being involved in criminal activities, had medical problems during treatment, had increased dosage during treatment and adherence to Methadone treatment. Determining appropriate doses for MMT patients and improvement in patient's adherence to Methadone are recommended to strengthen the effectiveness of MMT program.