The simultaneous determination of phenylurea and carbamate herbicides (diuron, linuron, siduron, methyldymron, chlorpropham, and swep) in water was studied using FRIT/fast atom bombardment (FAB)-liquid chromatography/mass spectrometry (LC/MS). These herbicides were extracted from water by the use of an octadecyl-silica solid phase extraction (SPE) cartridge, and then eluted from the SPE cartridge with acetonitrile. Ethyl-N-phenylcarbamate was added as an internal standard to the eluates and these herbicides were determined by the FRIT/FAB-LC/MS-selected ion monitoring (SIM) method. By this method, these herbicides were analyzed in river water, ground water and tap water to which the standard solution was added. These recoveries were more than approximately 90% and these standard deviations were less than 10%, respectively.