Objective : Interaction of warfarin with herbal medicines still remains controversial. The aim of this study was to examine the effect of herbal medicines which contain ginseng on PT INR in patients being treated with warfarin. Method : We studied patients who take herbal medicines which contain ginseng with warfarin during their hospitalization. We retrospectively investigated the effect of herbal medicines which contain ginseng. 10 patients were assigned to receive one of the following adjuncts: Group A (n=4) that received Bojungikkitang-gagam, Group B (n=2) that received Ukgunjatang-gagam, and Group C (n=4) that received Shihogyeji-tang, Gamiondam-tang, Gwininaanshim-tang, and Saengpe-san together. We then investigated changes of PT INR in each group. Result : In group A, there were diminutions of PT INR in 3 cases, and increment in 1 case. In group B, there were increments of PT INR in both cases. In group C, there were increments of PT INR in 3 cases and there was no big change in 1 case. Conclusion : In this study, we found that the interaction of combined herbal medicine is very complicated. So, we must study further more study about interactions of combined herbal medicine on PT INR.