Aims: To evaluate the clinical factors affecting daily and day-to-day glucose variability by using continuous glucose monitoring. Methods: We performed a cross-sectional analysis of patients with type 2 diabetes mellitus (T2DM) who underwent a glucagon stimulation test (GST) with 72 h of continuous glucose monitoring. Daily glucose variability was evaluated by mean amplitude of glycemic excursions [MAGE], percentage coefficient of variation for glucose (%CV), and day-to-day glucose variability (mean of daily differences [MODD]) by using continuous glucose monitoring. Correlations of clinical factors, including insulin secretion ability by the GST with MAGE, %CV, and MODD, were analyzed. Results: In 83 T2DM with insulin therapy, age and hemoglobin A(1c) (HbA(1c)) correlated with MAGE and %CV, fasting plasma glucose with MAGE and MODD, and increment of C-peptide immunoreactivity (Delta CPR) by GST correlated inversely with MAGE, %CV, and MODD. In 126 T2DM without insulin therapy, age, diastolic blood pressure, and triglycerides correlated with MODD, HbA1c with MAGE and MODD, and Delta CPR inversely correlated with %CV. Use of alpha-glucosidase inhibitors inversely correlated with %CV, whereas that of sulfonylurea was associated with MAGE and %CV. Conclusions: These results suggest that Delta CPR correlated with stability of glycemic control, whereas poorly controlled diabetes is associated with increase in glucose variability. alpha-glucosidase inhibitors may be superior to sulfonylureas in reducing the glucose variability in T2DM. (C) 2019 Published by Elsevier B.V.