Background: Malnutrition is a major threat to the health of HIV infected individuals and associated with increased risks of morbidity and mortality. The nutritional status (stunting, thinness) of HIV infected adolescents has a great impact on overall health, growth and development. Literature is dearth regarding the issue. Objective: To assess the prevalence of under nutrition and its associated factors among adolescents living with HIV in east Gojjam zone, Ethiopia, 2020. Methods: Institutional based cross sectional study was conducted among 300 adolescents living with HIV from March 25 to April 30, 2020 in East Gojjam Zone. All the study participants in the data collection time were included until required sample size was reached. Interviewer administered questionnaire was used to collect the data. WHO anthro plus was used to convert anthropometric data and analyzed by SPSS v- 23. Having a p-value < 0.05 in multivariable logistic regression analysis was used to conclude the presence of statistically significant association. Finally the results were presented by texts, tables and graphs. Results: A total of 300 adolescents living with HIV were participated (100% response rate). About 39% were stunted and 14% were thin. Being male was two times more likely to be stunted AOR=2.35, (95% CI: 1.30-4.26). Participants whose residence urban was 3.4 times more likely to be stunted AOR=3.4, (95% CI: 1.66-6.96). Participants who had not nutritional counseling were two times more likely to be stunted AOR=2.06, (95%CI: 1.05-4.03). Participants whose hemoglobin level ≥12mg/dl were 62% less likely to be stunted than their counter parts AOR= 0.38, (95% CI: 0.15-0.93) and Participants who didn’t skip their meal was 74% less likely to be stunted AOR=0.26, (95% CI: 0.13-0.50). Participants who were male were 2.73 times more likely to be thin (AOR=2.73, (95% CI: 1.07-6.95). Participants who didn’t Skip their meal were 76% less likely to be thin AOR=0.24, (95% CI: 0.08-0.69). Participants, with hemoglobin level1 ≥12mg/dl were 93% less likely to be thin (AOR=0.07, (95% CI: 0.025-0.23). Conclusion: The prevalence of stunting was (39%) and thinness was (14%) among the HIV infected adolescents. Sex, Skipping meal, residence, nutritional counseling and hemoglobin level were associated with stunting and thinness. Only increasing access to ART can’t solve problem of malnutrition, therefore nutrition counseling and support as an adjunct to the initiation of ART should be considered. adjunct to the initiation of ART should be considered. Key words: Under-nutrition, Adolescents, HIV/AIDS, Ethiopia.