Abstract: OBJECTIVE To establish adetection method for Panax quinquefolium a illegally added in Wuji Baifeng pills by UPLC-MS/MS. METHODS The analysis was performed on Waters ACQUITY BEH C₁₈ column(2.1 mm×100 mm, 1.7 μm), with acetonitrile-water as the mobile phase with gradient elution and the flow rate of 0.35 mL·min^-1. The column temperature was 40℃. The analytes were detected by tandem mass spectrometry with the electrospray ionization(ESI^-) source combined with multiple reaction monitoring(MRM) mode. RESULTS Psuedo-ginsenoside F₁₁ showed good linear relationship within the ranges of 0.113 0-451.9 ng·mL^-1(r=0.999), and the RSD of repeatability test was 3.5%. The average recovery(n=9) of pseudo-ginsenoside F₁₁ was 96.9%. The limit of detection was 0.1 ng·mL^-1 and the limit of quantitation was 0.4 ng·mL^-1. CONCLUSION The established method is fast and accurate with a high sensitivity and a high degree of separation. It can be used for the screening and detection of Panax quinquefolium illegally added in Wuji Baifeng pills.