Background: Diabetic Ketoacidosis (DKA) is one of the most serious acute complications of Diabetes Mellitus (DM) and the leading cause of morbidity and 9 mortality in children with type 1 diabetes. The mortality rate for DKA ranges from 2 to 5 % in developed countries and 6 to 24% in developing countries. Objectives: To assess the magnitude and associated factors of DKA in newly diagnosed Diabetic Mellitus children in Addis Ababa. Method: A facility based cross sectional study was conducted in selected hospitals in Addis Ababa. Data was double entered from the paper-based abstraction sheet into Epi info version 7 and exported to SPSS version 21 for analysis. A descriptive analysis was performed. Bivariate and multivariate logistic analysis was used to identify factors associated with the magnitude of newly diagnosed Diabetic Ketoacidosis. Categorical variables were compared if necessary using odds ratio with levels of significance set at 5%. Result: The magnitude of DKA in newly diagnosed children found to be 35.8%. The significant predictors of DKA among newly diagnosed children were age of the child, parents’ knowledge of the sign and symptoms of DKA 0.51(0.273, 0.95) sign and symptoms of DKA before the onset of DKA 0.348(0.206, 0.59) and infection prior to DKA onset 3.45(1.97, 6.04). Conclusion: The overall magnitude of DKA in children with newly diagnosed type 1 diabetes in Addis Ababa is low. In particular, children between 9-12 years of age and children whose parents don’t know the sign and symptoms of DKA have a high risk of DKA at primary diagnosis of DM. The Diabetic Association should give different workshop for health professional and work on awareness creation for the society using different communication media.