Background: Phlebitis is the inflammation of the vein and common complication of peripheral intravenous cannula. Phlebitis leads the patient to sepsis and pulmonary embolism that increase mortality. Incidence and median survival time of phlebitis varies across the world. The incidence, median survival time and predictors of phlebitis are not well addressed in Ethiopia. Therefore, this study focuses on the time to develop and predictors of phlebitis. Objective: Time to develop phlebitis and predictors among patients admitted in medical ward with peripheral intravenous cannula at public hospitals of Bahir Dar, Amhara, Ethiopia, 2022 Methods and Materials: An institution based prospective follow up study was conducted at public Hospitals of Bahir Dar city and 462 patients who were selected through systematic random sampling technique. Phlebitis was identified by Jackson’s Visual Infusion Phlebitis Scoring System. Cox proportional hazards regression model was used. Results: In this study, 462 patients participated, of those, 171(37.01%) acquired phlebitis. The median survival time to develop phlebitis was six days. Patients in age group > 60 years were 51% times (AHR = 0.49, 95% CI 0.29-0.82) less hazardous to acquire phlebitis than age group 15-40 years. Patients with Chronic-diseases were 1.50 times (AHR =1.50, 95% CI 1.09-2.07) more risk to acquire phlebitis as compared to patients with no chronic disease. The statistical interaction effect of drugs and blood showed that if drugs and blood administer in one vein, the hazards/risk of phlebitis increase by 2.03 times (AHR=2.03, 95% CI 1.44-2.86). Patients with inappropriate cannula dressing were 1.81 times (AHR=1.81, 95% CI 1.31-2.51) more hazardous to develop phlebitis as compared to with appropriate cannula dressing. Patients with large cannula size and cannula short dwelling time were 1.52 times (AHR = 1.52, 95% CI 1.08-2.15) and 7.39 times (AHR =7.39, 95% CI 4.12-13.32) more risk to acquire phlebitis as compared to patient with small cannula size and longer cannula dwelling time respectively. Conclusion and recommendation: the incidence density rate was 8/100 persons per day observation and the median survival time were six days. Younger age, chronic disease, using one intravenous line for more than one purpose, larger cannula size, inappropriate cannula dressing and longer cannula dwelling time were found as hazard/risk factors for phlebitis. Therefore, patients with those risk factors need to get special care and follow up. Keywords: Time to Develop, Predictors, Phlebitis, Peripheral Intravenous Cannula, Patients