Background: The term Malnutrition is strongly associated with children living with HIV AIDs, but it has not been well characterized in Ethiopia,which is likely to introduce a gap in the health care services provided to them. rnObjectives: This study proposed to assess undernutrition and associated factors among HIV positive children aged below 15 years attending in selected government Hospitals in Addis Ababa, Ethiopia. rnMethod; Institution based cross-sectional study was conducted among 238 HIV positive children below 15 years, who receive ART services in three selected Governmental hospitals. Systematic random sampling was used to select the study participant. Data was collected using structured questionnaire, through measurement of weight, height as well as MUAC, and through revision of medical record of the children. Data were analyzed using both univariate descriptive statistics and multivariate method. rnResults and discussion :The prevalence of stunting and wasting were 28.60% (95%CI:22.9%-34.8%) and 26.5% (95%CI:21.0%-32.6%) respectively. Variable like living with the virus for 5-10years [AOR=2.26 ,95%CI: 1.07-4.77], Family income