Inadequate self-management of diabetes has been a great concern due to its negative effect on the health and wellbeing of diabetic patients. Knowledge about diabetes mellitus and self-management has been low. The study assessed knowledge about diabetes mellitus and self-management among patients attending two teaching hospitals in Ogun State. Descriptive design was utilized. Populations were 110 and 90 patients attending Olabisi Onabanjo Teaching hospital and Babcock University Teaching Hospital respectively obtained from two weeks clinic record. Sample size was determined using total enumeration method. Researchers-designed questionnaire was used to collect data. More respondents in Olabisi Onabanjo Teaching hospital and Babcock University Teaching Hospital had high knowledge 79(97%),69(87%) about diabetes mellitus and low 39(48%) to moderate 45(57%) knowledge about prevention of diabetes respectively. There was significant difference in knowledge about dietary modification, lifestyle modification and glucose monitoring among respondents (p=0.000, p=0.000, p=0.000). There was no significant difference in knowledge about physical activity and pharmacological therapy among respondents (p=0.875, p=0.013). Knowledge about diabetes is moderate. Knowledge about dietary modification, lifestyle modification, glucose monitoring and pharmacological therapy among respondents is significantly different while knowledge about physical activity among respondents is not significantly different. More awareness should be created about diabetes self-management to improve patients’ knowledge.