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. Literature on Phlebitis is scanty in Ethiopia. Therefore, this study focuses on the time to develop (incidence) and predictors of phlebitis. 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. Age group > 60 years (AHR = 0.49, 95% CI 0.29-0.82) was preventive factor. Whereas, Chronic-diseases (AHR =1.50, 95% CI 1.09-2.07), drugs and blood administer in one vein (AHR=2.03, 95% CI 1.44-2.86), inappropriate cannula dressing (AHR=1.81, 95% CI 1.31-2.51), large cannula size (AHR = 1.52, 95% CI 1.08-2.15) and longer cannula dwelling time (AHR =7.39, 95% CI 4.12-13.32) found as risk factors of phlebitis.Conclusion and recommendation: 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 risk factors for phlebitis. Therefore, patients with those risk factors need to get special care and follow up.