The objective of this study was to compare the effects of gliclazide/metformin on glycemic control in patients with Type 2 diabetes mellitus uncontrolled on monotherapy with sulfonylurea or metformin. This was a prospective, open-labeled, multicentric study over 12 weeks. Patients who were diagnosed of Type 2 diabetes and were uncontrolled on monotherapy with oral hypoglycemic agents, including gliclazide and metformin, characterized by HbA1c 7% or greater and 10% or less and fasting plasma glucose (FPG) 140 mg/dL or greater were enrolled in this study. The treatment regimen was started at 80 mg gliclazide plus 500 mg metformin once a day and was titrated to the next dose level depending on the clinician's judgment, not exceeding a total daily dose of 320 mg gliclazide and 2000 mg metformin. Changes from baseline HbA1c, FPG, and postprandial glucose were examined. After 12-weeks treatment, the gliclazide + metformin combination showed improvement in metabolic control as assessed by changes in HbA1c, FPG, and postprandial glucose. The primary efficacy parameter, HbA1c, was significantly reduced to 7.35 ± 1.10 at the end of treatment from the baseline value (8.51 ± 0.77) (P < 0.001). A total of 84.35% of patients showed a 0.5% or greater reduction in HbA1c and 37.39% of patients reported less than 7% HbA1c at the end of therapy. FPG and postprandial glucose were significantly reduced at the end of therapy as compared with baseline values (P < 0.001). Moreover, the lipid profile was also improved during the treatment period. The addition of gliclazide to metformin is an effective treatment for patients inadequately controlled on sulfonylurea or metformin alone. A combination of gliclazide with metformin achieves good glycemic control and improves lipid levels with better tolerability profile.