Abstract: Type 2 diabetes mellitus (DM) has become a public health problem that seriously influences patients' quality of life. Identification of the level of knowledge related to diabetes among the general public is essential in strategies for prevention of diabetes mellitus. This study aims to assess the baseline levels of knowledge and its relation with glycated hemoglobin (HbA1c) level in diabetic patients in Taiz. The study was conducted on forty individuals with type2 diabetes of both sexes and used a questionnaire for data collection from Yemeni population than find the relationship between knowledge and HbA1c, blood glucose (BG) and Body Mass Index (BMI). Results showed significant differences (P < 0.05) in the knowledge, HbA1c, BG, and BMI between the samples studied, where demonstrated that 5% of samples was knowledge above 68 % and had a lower HbA1c level less than 6, also shown that 40% of the samples was knowledge 60 % with an average of HbA1c level 8%. In comparison, 32.5% of samples were knowledge less than 50% and had a high average HbA1c level 11%, also found there is a relationship between knowledge and BG, BMI, even the knowledge on the disease for males (52.81%) better than females (47.19%). Type2 diabetic patients have a decrease in knowledge, and this affects levels of HbA1c and BG, even who has good and moderate knowledge, not reflected on their attitudes towards HbA1c and BG.