A method of high performance liquid chromatography coupled with diode array detection and electrospray ionization mass spectrometry (HPLC-DAD/MS) in negative ion mode was developed for the analysis of ginsenosides in Sheng-Mai-Yin decoction (Panax gingeng C. A. Mey, Ophiopogon japonicus (Thunb.) Ker-Gawl, Shisandra chinensis (Turcz.) Baill.). The analyses were preformed on a reversed-phase C18 column (4.6 mm i.d. x 150 mm, 5 microm) using a binary eluent (10 mmol/L ammonium acetate (A) and acetonitrile (B), 1 mL/min) under gradient conditions (60% A - 40% A at 0 - 30 min, 40% A - 30% A at 30 - 40 min). Seventeen ginsenosides (20 (R) -Rh1, Rh2, Rg3, Rg2; 20 (S) -Rh1, Rh2, Rg3, Rg2; Rf, Rg6, Rg5, F4, Rk1, Rk3, Rh4; 20 (S)- and 20 (R) -protopanaxatriol) were well separated and detected at 203 nm by a DAD detector. The effluent from the DAD detector was introduced into the electrospray ionization (ESI) source in a post-column splitting flow rate at 0.3 mL/min. In the mass spectrum two major ions [M - H]- and [M + AcO]- were observed for ginsenoside standards (20 (R) -Rh1, Rg3, Rh2; 20 (S) -Rh1, Rg3, Rh2; 20 (S)- and 20 (R) -protopanaxatriol) and ginsenosides in Sheng-Mai-Yin decoction. Some other ions [M - Glc - H]-, [M - 2Glc - H]-, [M - Rha - H- and [M - Rha - Glc - H]- were also found in the mass spectrum of ginsenosides of Sheng-Mai-Yin decoction. In the decoction process ginsenosides changed into constituents of moderate and low polarity by hydrolysis, isomerization and dehydration at the site of C-20 and hydrolysis reaction also occurred at the site of C-3 or C-6. The work above presents a quick and accurate assay method which can could be used for the qualitative analysis of ginsenosides in Sheng-Mai-Yin decoction and the quality control of Sheng-Mai-Yin preparation.