Background: Microvascular angiopathies in DM patients are associated with elevated levels of glycated hemoglobin (HbA1c). However, the connection between HbA1.c and the severity of CAD and coronary perfusion in DM patients remains obscure. Objectives: Evaluation if there is a correlation between HbA1c levels and the complexity of coronary artery lesions, as measured by the Syntax score among middle-aged DM patients who have been referred for elective coronary angiography. Patients and Methods: 50 patients with type 2 diabetes participated in this prospective, randomized clinical investigation. Patients who voluntarily had coronary angiography at 6th October Insurance Hospital, Giza, Egypt between April 2021 and January 2022 were evaluated for coronary artery blockage. Results: Syntax score was highly statistically significant relation between Syntax score and HbA1c where Syntax score significantly increased among patients in group III (29.70±5.14) than patients in group II (14.53±4.42) and patients in group I (6.00±2.66), (P<0.001). Moreover, there were significant positive correlations between smoking and total cholesterol with Syntax score (P<0.05). However,no significant correlations were found between Syntax score with age, sex, HTN, serum creatinine, LDL, HDL, and triglyceride of the studied patients, (P>0.05). ROCcurve analysis shows that, the best cutoff value of HbA1c in detection of severity disease using syntax score was ≥6.95, with AUC=0.705, sensitivity 86%, specificity 73%, with significant level p=0.016 Conclusion: The severity of coronary artery lesions in diabetic patients was significantly linked with their HbA1c levels. Further, after accounting for other potential dangers, the HbA1c value was discovered to be a significant predictor of coronary artery lesion complexity.