Selecting tap water,sea water and the Organisation for the Prohibition of Chemical Weapons(OPCW) official test water as background matrices,a high performance liquid chromatography-quadrapole time-of-flight mass spectrometric(HPLC-Q-TOF /MS) method was developed for the determination of ricin on the base of instrumental parameter optimization.The limits of detection(LODs) of ricin were 0.05,0.20 and 1.00 μg/mL for the three matrices,respectively.The relative molecular mass of ricin was determined to be 62 884.97 Da.In order to improve the analytical sensitivity of complex water samples,immunocapture with magnetic beads linked by anti-ricin monoclonal antibody 6A6 was adopted to enrich and purify ricin in different water samplesELISA was used to draw the standard curve of immunocapture.The method showed a good linearity for ricin in the concentration range of 5.00-100 μg/mL.The average recoveries at spiked levels of 15,30 μg/mL were in the range of 82.1%-88.8%with RSDs of 4.2%-5.9%.The HPLC-Q-TOF/MS method with immunocapture was applied in the determination of ricin spiked in different matrices.The LODs for ricin in the three different matrices reached to 2.5，10，50 ng/mL,respectively.The results demonstrated that the method could be rapidly and effectively used in the determination of trace ricin in water samples.