Abstract: A method for determination of 6 cyclohexanedione herbicides, tepraloxydim, alloxydim, cycloxydim, tralkoxydim, sethoxydim and clethodim in rice and corn was developed. After homogenization, sample was extracted with acetonitrile. The extracts were cleaned by C₁₈ and Envi-Carb solid phase extraction (SPE) cartridge. Identification and detection were achieved by electrospray ionization (ESI) in positive mode using multiple reaction monitoring of liquid chromatography coupled with tandem mass spectrometry. The linearity of all the 6 cyclohexanedione herbicides in the range from 1 to 100 μg•L^-1 is correlation coefficient greater than 0.999. Cyclohexanedione herbicides are quantified by external standard method. Recoveries of 6 cyclohexanedione herbicides are within 70.0％-97.9％at the spiked levels of 5-20 ng•g^-1. The relative standard deviations (RSDs) for the 6 herbicides are less than 10%. 