Objective: We aim to evaluate longer term efficacy and safety of AG as an add-on therapy in patients with type 2 diabetes controlled by conventional treatment. Materials and Methods: A total of 23 type 2 patients are enrolled in the study. Utilizing a double-blind, crossover design, the participants are randomized to receive either placebo or American ginseng extract (AG) 1g/meal=3g/day for 8-week, while maintained on their conventional diabetes treatment. Following ≥4-week washout period the participants are crossed over to another 8-week treatment arm. Throughout the study period, all individuals maintain their original diabetes treatment and regular lifestyle. The primary endpoint is HbA1c, and secondary are fasting blood glucose and insulin, blood pressure, serum nitrates/nitrites (NOx) and PAI-1. Safety parameters include liver, kidney and hemostatic functions.