Background: Diabetes mellitus is one of the non-communicable chronic diseases that significantly increases morbidity and death in low- and middle-income countries like Ethiopia. Between 90 – 95% of all cases of diabetes that have been detected globally are type 2 diabetes. Preventive practice of diabetes is vital for directing behavioral changes in those without diabetes and those at risk the disease. Objective: To assess non-diabetic patients' preventive practice and associated factors regarding diabetes mellitus who are attending outpatient departments at Bahir Dar City comprehensive specialized Hospitals, Bahir Dar, northwest Ethiopia, 2022. Methods: A facility-based cross-sectional study was employed among 416 non diabetic patients of Bahirdar city compressive specialized hospitals from April 29 to May 27, 2022. An interviewer-administered questionnaire was used to collect the data and Epi-data version 4.6 used entered data then, exported to SPSS version 23 for analysis. Preventive practice which was greater than the mean considered as good preventive practice. To assess the degree of association between dependent and independent variables logistic regression was employed. The odds ratio with a 95% CI at a p-value <0.05 was used to declare the significance level. Result: Out of 416 non-diabetic patients who were visiting outpatient departments of hospitals 36.54%, (95% CI: 32%, 41%) had good preventive practice. Living urban [AOR=2.22; 95%CI (1.28,3.85)], primary school [AOR=3.2; 95%CI (1.22,8.22)], government employee [AOR=3.89; 95%CI (1.52,9.91)], family history of DM [AOR=3.94; 95%CI (2.14,7.24)], knowledge towards DM [AOR=2.68; 95%CI (1.55,4.65)], high perceived susceptibility [AOR=3.10; 95%CI (1.63,5.87)] and high perceived disease severity [AOR= 2.33, 95% CI (1.30,4.17)] were found to be statically significant with preventive practice towards DM. Conclusion: Level of preventive practice against diabetes was considerably low. Those who were being urban residence, primary school, government employed, have family history of DM and knowledge of DM, high perceived susceptibility and severity had good preventive practice against diabetes mellitus. Therefor health care providers better to give uninterrupted awareness creation health education for these group of patients attending outpatient departments of hospitals to enhance their knowledge towards diabetes. Keywords: Bahir Dar city, diabetes mellitus, health belief model, hospitals, outpatients, preventive practice.