Adherence to antiretroviral therapy is essential for achieving durable clinical outcomes in patients with HIV. In addition, suboptimal adherence can accelerate development of drug-resistant HIV and mitigate HAART’s role in reducing HIV incidence and transmission. The present research has been conducted to study treatment adherence and determine its effective factors on HIV/AIDS patients with the support of Ahvaz JundiShapur University of Medical Sciences in 2015. This is a cross-sectional study in which 158 HIV/AIDS patients who had been registered in the counseling centers of behavioral diseases of Ahvaz and were receiving antiretroviral treatment. They had been selected by census method. Data were collected using the AACTG (Adult Aids Clinical Trials Group) questionnaire. The collected data was analyzed and interpreted using descriptive statistical tests, χ2 and step by step regression by spss-16 software. The mean age of patients was 32.8±10.36. Among them 20.8% were female, 47.5% were single and 35.6% had a job. Also 33.7% of the respondents had CD4+ cell count less than 350 cells/μL. and average treatment duration was 9 months at study entry. According to the findings of this study, the degree of adherence was reported as % 63.9.The main reasons for non-adherence were forgetfulness (26%) and side effects (19%). There were no significant differences between highly adherent and less adherent patients with regard to age, gender, education Employment status, Treatment duration, time of diagnosis. Adherence to HAART is a key factor in disease course in persons with HIV/AIDS. Low-level adherence in subjects of the study indicated that educational and intervention is quite necessary for patients in order to improve their medication self-management.