Access to antiretroviral therapy and Human immunodeficiency virus (HIV) care is increasing in resource-limited settings like Tanzania. This study was conducted to evaluate prevalence and risk factors associated with treatment failure, in HIV patient on Anti Retroviral Therapy (ART) for more than six months in Dar es Salaam. A cross-sectional observational study that involved 70 conveniently sampled and consented HIV-infected patients who were on antiretroviral therapy for more than six month at PASADA Care and Treatment Centre (CTC) in Dar es Salaam. The findings of this study indicated that majority of Patient 78.5% (n=55) were experiencing ARVs benefits, they attained total viral suppression (<400 viral copies/ml. Ten percent (n=7) of patients were reported to have virological failure suppression (>10,000 viral copies/ml), and 10.4% (n=8) of them found to have partially viral suppression (400-9999 viral copies/ml). On the other hand, 27.1% (n=19) of participants were reported to have an immunological failure. Poor adherence to the treatment regime and drug toxicity were the main factors observed to associate with treatment failure in this study (P<0.05). Although many HIV-infected patients attending CTC in Dar es Salaam had advanced HIV infection, the majority of patients who were receiving antiretroviral therapy were experiencing viral suppression and clinical benefit. In order to optimize the likelihood of viral suppression and prolong benefits of improved quality of life to those HIV patients on ART attending CTC, early HIV testing, initiation of therapy with a potent, durable regimen, accompanied by stable drug supplies and proper counselling on drug adherence are important. Furthermore prospective studies on treatment failures, factors associating with treatment failures and studies that will aim at developing low-cost molecular methods to identify virological failure and ARV sensitivity were urgently needed.Welcome Trust through SACIDS.