Purpose: In this study, we investigated anti-thrombotic effects of Gamihyunbooleekyungtang currently used clinical treatment of dysmenorrhea and compared effects by decoction methods. Methods: Gamihyunbooleekyungtang was extracted by pressure extractor (GHYT) and nonpressure extractor(GHYT-1). Inhibitory effect of platelet cohesion, suppression effect of GPIIb/IIIa activity, inhibitory effect of $TXB_2$ and $PEG_2$ biosynthesis, and oxidative damage suppression effect were tested in vitro. Also suppression of pulmonary embolism was studied in vivo. Results: In this study, both GHYT and GHYT-1 extract showed a safety in cytotoxicity of hFCs. Both showed dose-dependent inhibitory effect on platelet coagulation. GHYT-1 extract is usually higher than GHYT, especially for $E_{max}$. GHYT and GHYT-1 extract showed dose-dependent inhibitory effect on GPIIb/IIIa activities. GHYT extract suppressed significantly $TXB_2$ biosynthesis at 1000, 500 ${mu}g/m{ell}$ and also suppressed significantly $PEG_2$ biosynthesis at 1000 ${mu}g/m{ell}$ as compared with the control group. GHYT-1 suppressed significantly $TXB_2$ biosynthesis at 1000${mu}g/m{ell}$ as compared with the control group. Also it suppressed pulmonary embolism triggered by collagen and epinephrine by respectively 50%, 75% as compared with the control group. Both GHYT and GHYT-1 extract showed dose-dependent decrease of oxidative damages caused by DPPH, whereas dose-dependent increase of superoxide dismutase like activity was observed. Conclusion: These results suggest that Gamihyunbooleekyungtang can be used for treating dysmenorrhea caused by thrombosis. Nonpressure decoction method is a little more effective, but more detailed studies would be needed.