Background: Under nutrition in surgical patients is found to be associated with reduced wound healing, increased complication rates, length of hospital stay, mortality, and healthcare costs than normally nourished patients. Several malnutrition cases have been reported from the routine care in the hospital. However, there is no study conducted in the study area. Objective: To assess the Prevalence of malnutrition and associated factor among elective surgical patient at TGSH Bahir Dar Ethiopia 2022 Methods: Hospital based cross sectional study was conducted among 328 consecutively admitted Elective surgical patients in TGSH Hospital from January 2022-August 2022 G.C. Data was collected using pre tested structured questionnaire. Anthropometric measurements and post-operative outcome assessment were made at admission and discharge of the patient. Data were entered and analyzed Using SPSS version 2021 software. Descriptive studies such as frequencies, percentages, mean and quantitative measure was done. Binary logistic regression was used to explore prevalence of under nutrition in elective surgical patient and associated factor. Result was presented using AOR with its 95% confidence level and P-values < 0.05 were declared statically significant. Results: A total of 122(37.2%) study participants were underweight at admission. Patients with Urban residence (AOR= 0.395; 95%: CI 0.221, 0.78), no previous operation (AOR=0.214; 95% CI 0.093, 0.492) patients with no comorbidities (AOR= 0.241; 95 CI: 0.105, 0.556), those with no surgical site infection and participants with length of hospital stay <= 7days (AOR=0.370; 95% CI 0.209-0.657) were factors less likely to be undernourished at admission. Conclusion: In the current study under nutrition is highly prevalent among surgical patients. Rural residence, previous operation and underlying comorbidities were common factors associated with under nutrition at admission and discharge. In addition, surgical site infection and length of hospital stay were identified factors at time of discharge. In patient with under nutrition the incidence of surgical site infection, length of hospital stay and comorbidities increases in comparison to those with no under-nutrition. The overall mortality found in this study was relatively higher compared with some studies in Ethiopia even if it is lower in some areas. Keywords: Malnutrition, prevalence, associated factor, Hospital