Background: Diabetes mellitus (DM) is a common, chronic, metabolic disease characterized by hyperglycemia as a cardinal biochemical feature. It has acute and chronic complications which significantly contribute to the morbidity and mortality in such patients. Knowledge about the disease is important for proper self-management and is the foundation of diabetes treatment. Children and adolescent living with diabetes must have sufficient knowledge of diabetes. Objectives: To assess diabetes knowledge among diabetic children and adolescent and its effect of glycemic control in children and adolescent attending diabetic clinic at HUCSH Methods: A facility based cross-sectional study design was conducted among children and adolescent with diabetes attending paediatrics diabetic follow up clinic of Hawassa university comprehensive specialized hospital from May 5 , 2022 to September – 5, 2022. A total of 107 children and adolescent with diabetes was included in the study which is selected by systematic random sampling technique. Knowledge of diabetes was evaluated by using Diabetes knowledge questioner and HbA1C results obtained from patient record. The data on the questionnaire was entered into SPSS and analyzed. Result: The study included 107 children and adolescents, of whom 52.3% were females. 49.5% of participants were aged between 8 and 14 years. Most of participants were middle in birth order (44.9%). Most of participants’ mothers have secondary school (29%) and most of participants’ fathers had university education (35.5%). Almost all participants’ father has occupation and 57% of participants’ mother has no occupation. About half of the participants (49.5%) had good knowledge levels. Sex of the patient [AOR = 5.407(95%CI = 0.998, 29.289)], Average monthly family income [AOR = 13.512(95%CI = 2.975 – 61.378)], HgbA1c level [AOR = 0.118(95%CI = 0.029, 0.478] were significantly associated with diabetes knowledge. Conclusion: The study found positive associations between diabetic knowledge and socio – demographic factors, as well as better glycemic control. Poor glycemic control was prevalent in children and adolescents with diabetes. Knowledge about the causes, control, self-monitoring and other self-care measures especially with regard to preventive measures were specific aspects of diabetes that need to be further strengthened among the diabetic patients. Recommendation: More efforts are required to scale up the diabetes knowledge among children and adolescents. Further, a deep and well-designed study that includes a quantitative and qualitative approach is recommended to address other hidden factors that are associated with diabetes knowledge.