Background: Nutritional support is identified as one of the most critical and immediate needs for people living with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). Adequate nutrition is vital to optimize response to medical treatment, manage opportunistic infections, maintain the immune system, and support optimal quality of life for people living with HIV/AIDS (PLWHA). Evidence has shown that the progression of the disease could be slowed with good nutrition. Nutrition interventions increase compliance with treatment regimens and optimize the benefits of antiretroviral drugs. The nutritional knowledge, dietary practice and associated factors among adults on antiretroviral therapy are not well understood generally in Ethiopia and particularly in Bahir Dar City. Therefore, the aim of this study was to assess the nutritional knowledge, dietary practice and associated factors among adult PLWHA on anti-retroviral therapy (ART) in Felege Hiwot Referral Hospital. Methods: Institution based cross-sectional study was conducted from April 13 to May 18, 2017 in Felege Hiwot Referral Hospital. Systematic random sampling technique was used to select 539 adults on highly active antiretroviral treatment (HAART). Data were collected using a semi-structured and pretested questionnaire. Bivariate and multivariate logistic regression analyses were carried out to identify factors associated with nutritional knowledge and dietary practice.Results: This study shows that 25.8, 52.5 and 21.7% of respondents had poor, average and good nutritional knowledge scores respectively. Ever heard about good nutrition and received dietary counselling were significant factors for nutritional knowledge. This study also reveals that 3.2, 66.4 and 30.4% of respondents had poor, average and good dietary practice scores respectively. Presence of gastrointestinal symptom, ever heard about good nutrition and good nutritional knowledge were significant factors for dietary practice. Conclusions: This study found that the magnitude of good nutritional knowledge and good dietary practice were 21.7 and 30.4%. Nutrition education and counseling should be given by health care workers for patients on ART to improve their nutritional knowledge. The media should also strengthen its role in disseminating nutrition information. The health professionals should routinely diagnose and treat gastrointestinal symptoms to maintain patients' appetite for food their by increasing dietary intake.