Background: The endothelial dysfunction was greater by glucose fluctuation than by chronic hyperglycemia. The glycemic variability (GV) may be an independent risk factor for atherosclerotic coronary artery disease in diabetic patients. The cardiovascular complications are higher following myocardial infarction in diabetic patients than nondiabetic individuals. Aim of the Work: Our aim is to prove that good controlling of acute shooting of blood glucose level up and down will improve the outcome in patient undergoing percutaneous coronary intervention (PCI). Subjects and Methods: GV is evaluated using intraday variability by fasting, preprandial, and postprandial blood glucose levels in 120 patients. Hemoglobin A1c was used to evaluate glycemic control. The relationship between GV and development of major adverse cardiac events (MACE) in patients undergoing PCI is studied. Results: There is a statistically significant difference between the relation of GV and MACE within 1 month after PCI in uncontrolled diabetes compared to controlled group. There is no statistically significant difference found between the two groups regarding age, gender, risk factors (hypertension, smoking and dyslipidemia), and laboratory parameters including triglycerides, total cholesterol, low-density lipoprotein, and high-density lipoprotein. Conclusions: Uncontrolled GV is associated with poor short-term outcome after PCI in controlled diabetic patients compared to nondiabetic individuals undergoing PCI. Greater GV is associated with composite MACE, especially for uncontrolled diabetic patients. After multivariable logistic analysis, GV remains an independent prognostic factor for composite MACE after 3 months in patients under going PCI. Keywords: Glycemic variability, hemoglobin A1c, intraday variation, major adverse cardiac events