A liquid chromatography-tandem mass spectrometric(LC-MS/MS) method was developed for the detection of three brevetoxins,i.e.BTX-1,BTX-2 and BTX-3 in seawater based on liquid-liquid extraction.The analysis volume of seawater was reduced to 20 mL by using LC-MS/MS.The extraction conditions for three brevetoxins in seawater optimized with response surface were as follows:sodium chloride:6 g,vortex time:60 s,extraction solvent:5 mL ethyl acetate;and extraction times:twice.The linear ranges of three brevetoxins were all 1-200 μg/L,their limits of detection and quantitation were 0.02 μg/L and 0.05 μg/L,respectively.The average recoveries for three brevetoxins ranged from 95.4% to 104%,with intra-day and inter-day relative standard deviations(RSD) of 2.2%-5.3% and 3.0%-4.5%,respectively.With low consumption and high pretreatment efficiency,this method realizes the rapid analysis on trace of brevetoxins in seawater.