Abstract: Eucommia ulmoids is a kind of traditional Chinese herbal medicine. Aucubin (AU), chlorogenic acid (CA), geniposidic acid (GA) and geniposide (G) are important components in E. ulmoids. A HPLC-MS/MS method was established to determine these four target chemicals in E. ulmoids. Chromatographic conditions were: the chromatographic column XD-C18 was adopted, the mobile phase was 0.1% formic acid aqueous solution and methanol, the flow rate was 0.15mL/min, and the column temperature was 30℃. Mass spectrometry conditions were: ESI ion as a pyrolysis source, the pyrolysis temperature was 280℃, the source voltage was 4kV, sheath gas was nitrogen, flow rate was 30psi, the atomization gas was helium, and the flow rate was 10psi. The R2 of CA, AU, G and GA standard curve were 0.9935, 0.9942, 0.9969 and 0.9948, respectively. Lower limit of detection was from 7.603 to 8.853pmol. Spiked recovery was from 91.838% to 108.326%. In E. ulmoids, the content of AU was 20.552±4.032ng/mg dry weight (DW), the content of GA was 6.913±0.654ng/mg DW, the content of CA was 25.986±3.412ng/mg DW, and the content of G was 0.205±0.015ng/mg DW. This method was also used to determine the contents of these four target chemicals in other seven plant species, and the results indicated that the method is effective and widely applicable.