Objective: We studied the association between cardiac autonomic function and glycemic variability in patient with type 1 diabetes. Methods: A total 45 type 1 diabetic patients (mean age 37.5 ± 11.5 years, 51% male, mean diabetic duration 8.6 ± 6.1 years, mean Hemoglobin A1c 7.9 ± 1.2%) without cardiovascular disease underwent continuous glucose monitoring (GGM) and ECG recording, simultaneously and continuously, for 72 hours. Glycemic variability (GV) was calculated by the standard deviation (SD), coefficienct of variation (CV) of glucose, average daily blood glucose range (maximum - minimum value of blood glucose per day) and the mean amplitude of glycemic excursion (MAGE) in CGM. Cardiac autonomic neuropathy was measured by analysis of heart rate variability (HRV) in time and frequency domains. Results: After adjustment for HbA1c and diabetic duration, normalized low frequency of heart rate variability was inversely correlated with the average daily blood glucose range (r = - 0.328; P = 0.036). No significant association was found between HRV parameters and SD, CV and MAGE in CGM. Conclusion: Increased GV is associated with reduced HRV independent of HbA1c level and the duration of diabetes in type 1 diabetes. This study suggests that GV may associated with cardiac autonomic dysfunction in patients with type 1 diabetes.