Objective: Few data were available on glycemic control at the early prediabetic stage, though it is the important stage to prevent diabetes mellitus. The purpose of this research was to examine the glycemic control effects of herb medicine treatment (DA-9802) in prediabetic stage patients Methods: In this randomized, single blind, placebo-controlled study, we compared Sanyak extract (DA-9802) with placebo for the treatment of glycemic control effects in prediabetic stage patients. 45 volunteers who satisfied the requirements were enrolled in the study. They took Sanyak extract (DA-9802) or placebo treatment three times a day for 8 weeks. Blood sugar, Total Symptom Score (TSS) and blood serum were measured at weeks 0, 4, and 8. Results: In the DA-9802 group, fasting blood sugar changes between before 8 weeks significantly decreased. Fasting blood sugar, fasting blood sugar gaps between before and after treatment for 8 weeks, insulin changes and C-peptide significantly decreased at 8 weeks compared with those of the placebo group. Conclusion: Herb medicine treatment (DA-9802) is effective in glycemic control on prediabetic stage.