Object To isolate the active compounds on reversing multidrug resistance (MDR) of tumor cell from the ethanol extract in the seeds of Cnidium monnieri (L ) Cuss Methods The fractionation directed by bioactivity was carried out with silica gel chromatography and RP HPLC Results Three active coumarins were obtained: imperatorin (Ⅰ), edultin (Ⅱ) and 3′ isobutyryloxy O acetyl columbionetin (Ⅲ) Their sturctures were identified by spectroscopic analysis Conclusion These three compounds have a medium reversing MDR of KBV200 in vitro