Present study investigated the effects of the 70% ethanol extracts of tissue-cultured mountain ginseng (TCMG), Korean red ginseng (KRG), and Panax ginseng (PG) on agonist-induced platelet aggregation and activation in human whole blood. The $IC_{50}$ values for TCMG, KRG, and PG were 1.159, 3.695, and 4.978mg/mL for collagen-induced aggregation, 0.820, 2.030, and 4.743mg/mL for arachidonic acid-induced aggregation, and 1.070, 2.617, and 2.954 mg/mL for ADP-induced aggregation, respectively. Also, this study assessed the effects of the most active extract, TCMG, on markers of platelet activation by determining receptor expression on platelet membranes in healthy subjects, including expression of GPIIb/IIIa-like (PAC-1) and P-selectin (CD62), by flow cytometry. A significant decrease in PAC-l expression (p=0.018) was observed in the presence of TCMG. These results show that TCMG has potent anti-platelet activity.