ABSTRACT OBJECTIVE：To establish a method for content determination of paclitaxel in malignant ascites of tumor patients. METHODS：LC-MS/MS method was adopted. Using vindoline as internal standard，the content of paclitaxel in ascites of tumor patients was determined. The separation was performed on Zorbax SB-C18 column with mobile phase consisted of aqueous solution （containing 0.1％ formic acid and 10 mmol/L ammonium acetate）-acetonitrile（40 ∶ 60，V/V）at the flow rate of 0.25 mL/min. the column temperature was 30 ℃，and sample size was 5 μL. The ion source was electrospray ion source，and the detection mode was multiple ion monitoring positive ion mode. MS parameters were set as following as dry gas temperature 350 ℃，dry gas flow rate 10 L/min，capillary voltage 4 000 V. Quantitative determination was operated in the multiple reaction monitoring（MRM）mode， with the ion transitions m/z 876.5→308.0 for paclitaxel and m/z 457.3→188.1 for the internal standard. The fragment voltage/ collision energy for paclitaxel and the internal standard were 250 V/30 eV，and 150 V/20 eV，respectively. RESULTS：The linear range of paclitaxel were 25-2 500 ng/mL（r2＝0.996 5，n＝7）. The lowest limit of quantitation was 25 ng/mL. RSDs of inter-day and intra-day precision tests were 0.61％ -3.62％（n＝5，3）. Accuracies were 95.34％ -98.76％（n＝5，3）. RSDs of extraction recovery were 3.19％-3.72％（n＝3）. CV of matrix effect were 1.52％-2.93％（n＝3）. RE of stability tests were lower than 3％（n＝ 3）. CONCLUSIONS：The method is simple，accurate and suitable for the content determination of paclitaxel in malignant ascites of tumor patients.