An HPLC–ESI-MS/MS method was established to identify the absorbed components and metabolites in rat plasma after oral administration of Rhizoma Chuanxiong decoction (RCD), a well-known traditional Chinese medicine. By comparing the extracted ion chromatograms (EICs) obtained from dosed rat plasma, blank rat plasma and RCD, a total of 25 compounds were detected in dosed rat plasma. Among them, 13 compounds were absorbed into rat plasma in prototype and identified as ferulic acid, senkyunolide J, senkyunolide I, senkyunolide D or 4,7-dihydroxy-3-butylphthalide, senkyunolide F, senkyunolide M, senkyunolide Q, senkyunolide A, E-butylidenephthalide, E-ligustilide, neocnidilide, Z-ligustilide, levistolide A, according to the retention times, UV, MS, MS/MS spectra. In addition, 12 conjugated metabolites including 6 senkyunolide I-related metabolites, 4 senkyunolide J-related metabolites and 2 butylidenephthalide-related metabolites were also detected and identified by comparing their MS, MS/MS spectra with that of corresponding original components. Conjugated with glutathione, cysteine, glucuronic acid and sulphuric acid were the main metabolic reactions of phthalides. Finally the in vivo metabolic pathways of chemical constituents of Chuanxiong in rat plasma were proposed in this study.