Abstract: OBJECTIVE To establish an HPLC-MS/MS method for the determination of N-ethyl tadalafil which was added illegally into traditional Chinese medicines (TCM). METHODS The experiment steps was as follows:N-ethyl tadalafil was preliminary screened firstly by DAD detector, and then confirmed by mass spectrometer detector and quantitative determined by DAD detector at last. The preliminary screening and qualitative analysis was performed by HPLC-DAD, which was conducted on a SHISEIDO C₁₈ column(250 mm×4.6 mm, 5 μm) with gradient elution at a flow rate of 1 mL·min^-1. The mobile phase A consisted of water containing 0.7% triethylamine(adjusted to pH 2.8), methanol and acetonitrile (60:20:20); the mobile phase B consisted of water containing 0.7% triethylamine (adjusted to pH 2.8), methanol and acetonitrile(8:46:46). The sample was detected at 230 nm. The confirming test was performed by LC-MS/MS, which was conducted on a Dikma Spursil C₁₈ column(150 mm×2.1 mm, 3 μm) at a flow rate of 0.2 mL·min^-1 with mobile phase consisted of methanol-acetonitrile-0.02 mol·L^-1 ammounium acetate (contained 0.1% acetic acid) (30:25:45). RESULTS The linear relationship was good at the range of 0.003-0.3 mg·mL^-1, and the average recovery was 97.8%(n=9) with RSD of 0.7%. It was confirmed that N-ethyl tadalafil was added illegally in two batches of sthenic TCM through screening 30 batches of TCM, and the content of N-ethyl tadalafil was 4.8 mg·g^-1 and 4.1 mg·g^-1, respectively. CONCLUSION The method is fast, accurate and highly sensitive and can be used to screen the illegally sthenic TCM spiked with N-ethyl tadalafil.