Antiretroviral treatments adverse effect is one of the challenges in HIV/AIDS prevention and control programs. The major objective of this study was assessment of the level of ART adverse effect and its associated factors among people living with HIV (PLWH) on ART in Debre Markos Referral Hospital from October 2 to November 30/2013. Institutional based cross-sectional quantitative type of study design was conducted to determine the level of ART adverse effect among randomly selected 373 adult PLWH on ART in Debre Markos referral hospital. The study participants were selected using systematic random sampling technique. Both primary and secondary data were gathered using a structured questionnaire. The collected data were entered, processed and analyzed in STATA V.11. The period prevalence of ART adverse effect was 51. 4%. The most common type of adverse effect was lipoathrophy (37.5%, n=72) and the least was Hepathotoxicity (0.52 %, n=1). The odds of ART adverse effect were 0. 523 times less likely among those who were literate compared to illiterate [AOR=0.477, 95% CI=0.28-0.812]. similarly, it was 0.44 times less likely among the study par-ticipants with preparatory school level of educational status compared to those with primary school [AOR=0.56, 95% CI=0.443-0.953]. The odds of ART adverse effect were 0.725 times less likely among those had a monthly income of ≥ 3551 Ethiopian Birr compared to those had no a regular monthly income [AOR=0.275,95%CI=0.098-0.773] and were 0.546 times less likely among substance non-abusers than abusers [AOR=0.454,95%CI=0.253-0.817]. The prevalence of ART adverse effect in Debre Markos referral Hospital was found. The leading adverse effect was Lipoathrophy. Factors such as educational status, income and substance abuse were identified independent determinants of ART adverse effect. The program managers, implementers and service providers need to take in to consideration the emerging need of adult education, health education and creation of income generating activities for adult PLWHs on ART in Debre Markos Referral Hospital. Furthermore it is better to disseminate information on the possible Antiretro-viral therapy adverse effects using leaflets and patient- physician regular education program.