Interest in finding natural antioxidants for use in food or medical materials to prevent free radical imbalance has increased considerably over the past years. The aim of this research was to evaluate changes in glycemic control and psychological state of patients with type 2 diabetes mellitus (T2DM) after use of antioxidant plant preparations. Fifty-six patients with T2DM were randomly allocated to receive standardized Ginkgo biloba L. leaves dry extract, green tea dry extract, or placebo capsules. Diabetes glycemic control measured as glycated hemoglobin (HbA1c) level, antioxidant state and psychological data were evaluated at baseline, after 9 and 18 months of using either antioxidant preparations or placebo. The level of perceived stress lowered significantly after 9 months (p = 0.038) and 18 months (p = 0.030), and the psychological aspect of quality of life significantly improved after 18 months (p = 0.019) of use of G. biloba extrac. No significant differences were detected after using green tea extract. In patients using placebo, significant lowering of HbA1c level was observed after 18 months (p = 0.017). In conclusion, antioxidant G. biloba leaf extract exhibited a mild effect on psychological state and a trend of improving glycemic control in patients with type 2 diabetes mellitus.