Abstract: Sample decomposition method with alkaline CuO oxidation procedure in determination of lignin in sediment samples, firstly developed by Hedges and Ertel in 1982, has been improved. Sediment samples were decomposed with oxidative-alkaline CuO in a microwave-assisted digestion system and then lignin monomers were determined by gas chromatography. The factors affecting the oxidative decomposition efficiency of the lignin, such as digestion temperature and time, were investigated. The experiment results indicated that the best decomposition condition was 150℃ for 90 min. Under the optimized condition, recovery for lignin monomers was 91.4%~108% with average precision of 4.5%RSD. The proposed method provides the advantages of high efficiency, convenient for reaction condition control and has been proved to be an ideal method for the determination of lignin monomers in sediment samples.