Background: HIV/AIDS and malnutrition effect are interrelated and exacerbate one another in a vicious cycle. Malnutrition is serious problem of People Living with HIV and it is a silent factor that delays treatment outcomes. Currently due to the advent of antiretroviral drug therapy and subsequent improved life expectancy, HIV has become a chronic disease. Long term complications related to diet overweight and obesity has gained a new importance. Objectives: To assess prevalence of malnutrition and associated factors in adult PLWHA on ART in Arada sub-city, A.A, Ethiopia Methods and data analysis: Facility based cross sectional study design and systematic sampling method was used to get the study subjects and a structured pre-tested questionnaire was used to collect data. Logistic regression analysis was used to identify factors associated for malnutrition. Result: A total of 457 PLWHA were approached and 432 consented to participate in the present study giving a response rate of 94.5%. The overall under nutrition in the study participants were 53(12.3%) and over nutrition 82(19.0%).Two meals and below in the last six month 3.7 times more likely to expose under nutrition than three meals and above (95%CI (1.46, 9.48)). Weight loss >5% in the last six month 3.6 times more affected by under nutrition than weight loss ≤5%(95%CI(1.26,10.72)).Getting nutritional support 3.4 times likely to expose under nutrition(95%CI(1.33,9.04)). Not changing feeding style after HIV was 3.3 times more likely to develop under nutrition(95%CI(1.40,7.83)).WHO stage 2 and above 8.8times more affected by under nutrition than stage one(95%CI(2.24,34.69)). Female participants were 4.3times affected by over nutrition (95%CI(1.93,9.57)).Having another medical follow up was 6 times expose to over nutrition(95%CI(2.48,14.55)) .Those who had their Owen drinking water pipe 2.6 times more vulnerable to over nutrition(95%CI(1.38,5.06)) Conclusion: The prevalence of overall malnutrition in the study was 31.3% (under nutrition 12.3% and over nutrition 19.0%). Factors associated to under nutrition were body weight loss, nutritional support, stage of HIV and change of feeding after HIV/AIDS. Factors associated to over nutrition were sex, another medical follow-up, drinking water source and family size.