This study was performed to elucidate the influence on the plasma decursinol concentration after administration of combined decursin and Cnidii Rhizoma or decurisin and Bupleuri Radix extracts in comparison with single decursin administration. The identification of decursinol isolated from Angelica gigas was carried out by GC/MS and the concentration of decursinol in the plasma after oral administration was determined by HPLC. The value of area under the plasma concentration (AUC) and the maximal concentration (Cmax) of decursinol after administration of methanol and ether Angelicae Gigantis Radix extract was higher than those of single decursin-treated group. It was also found that the AUC and the Cmax of decursinol after combined administration with decursin and Cnidii Rhizoma were higher than those of decursin administration, whereas those of combined with decursin and Bupleuri Radix was lower. Moreover, the studies were performed with decursinol only or with combined decursinol and Cnidii Rhizoma/Bupleuri Radix, both of combined treatment increased the plasma decursinol concentrations compared with decursinol-treated group in rats. On the basis of these results, it is concluded that co-existing substances or co-administration with other drugs may influence the plasma levels of decurisinol after oral administration.