Background:The 30 mg pioglitazone tablet was recently introduced in Korea; no study has yet compared its glucose-lowering or weight gain effects to the 15 mg tablet in Korean patients with type 2 diabetes mellitus (T2DM). Methods: The electronic medical records of 45 patients with T2DM with glycated hemoglobin (HbA1c) levels > 7.0%, despite taking 15 mg/day pioglitazone and a stable dose of other diabetes drugs for 3 months, were retrospectively reviewed. Results: After dose up-titration, HbA1c levels decreased at 3-and 6-month follow-ups compared with baseline (8.5% at baseline vs. 8.2% at 3 months vs. 7.9% at 6 months; baseline vs. 3 months, P = 0.106; baseline vs. 6 months, P = 0.005; 3 months vs. 6 months, P = 0.096). In the subgroup analysis of 36 patients taking pioglitazone, sulfonylurea, and metformin, HbA1c levels also decreased at 3-and 6-month follow-ups compared with baseline (8.5 % vs. 8.2 % vs. 7.9%; baseline vs. 3 months, P = 0.289; baseline vs. 6 months, P = 0.014; 3 months vs. 6 months, P = 0.232). There was no significant body weight change (70.8 kg vs. 70.7 kg vs. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.