Fourier-transform infrared spectra (FTIR) was used to study the characteristics of dissolved organic matters (DOM) extracted from rice straw at different decay stages. The results showed that there were three stages for the dynamic change of DOM properties during decay: at the first stage (0-3 d), the low-weight-molecular sugar, amino-acid diminished rapidly due to the microorganism growth; at the second stage (3-63 d), the content of polysaccharides and aliphatic hydrocarbons in DOM leveled off in a range which was caused by the decomposition of hemi-cellulose and cellulose; after 63 d, it was the humification stage of DOM indicating by the polymerization of carbohydrates and aliphatic hydrocarbons based on the core of aromatic rings, which induced the more complicated molecular structure of DOM. At different stages, the structural properties of the fractions varied with decay indicating by the decrease of polysaccharides and increase of aromatic components.