Introduction: Although reduction in the incidence of nocturnal hypoglycemia, as estimated by symptom or self-monitored plasma glucose, was shown to be more pronounced with 300 units/mL insulin glargine (Gla-300) than with 100 units/mL insulin glargine (Gla-100) in type 2 diabetes patients, the exact frequency of nocturnal hypoglycemia estimated with continuous glucose monitoring (CGM) has not been reported. Methods: Forty patients with type 2 diabetes who were admitted for glycemic control with basal–bolus insulin therapy (BBT) were randomized into the Gla-100 and Gla-300 groups. Insulin doses were adjusted to maintain blood glucose levels within 100–120 mg/dL at each meal. Plasma glucose and C-peptide profiles were estimated serially after admission and before discharge. Daily CGM was also performed before discharge. Results: In the Gla-100 and Gla-300 groups, the mean duration of hospitalization was 15 ± 2 and 15 ± 1 days, respectively, and the mean basal insulin dose before discharge was 13 ± 7 and 15 ± 10 units, respectively. The dose of meal-time insulin was not different between the two groups. Compared with the Gla-300 group, the Gla-100 group had significantly lower nocturnal profiles of plasma glucose and C-peptide, but significantly higher frequency of CGM-estimated nocturnal hypoglycemia (10.7% ± 18.4% versus 1.2% ± 3.6%, P = 0.033). Conclusion: In type 2 diabetic patients, reduction in the incidence of CGM-estimated nocturnal hypoglycemia by BBT under tightly controlled diet therapy was higher with Gla-300 than with Gla-100. Trial Registration: UMIN clinical trials registry (UMIN000023360).