Abstract: The aim of this study is to analyze the effects of soil partic les on decomposition of organic matter derived from crop residues at a nanometer scale. Nanometer aqua w ithdrawn from layer B of black soil was put into the decomposing straw, several kinds of decomposed o rganic fractions at stages of different incubation time were analyzed by K₂Cr₂O₇-H₂SO₄ titration and infrared spectroscopic analysis. The results sho wed that there was great difference between control and treatment. Nanometer par ticles could significantly restrain the development of water soluble organic materials at prophase and anaphase of decomposition，pr omote the formation of little molecule organic materials, and decrease the content of water soluble humic acid. In addition, nanometer particle promoted fo rmation of alkali soluble organic materials and fulvic acid at prophase of decom position but had no significant influence on them at anaphases. The infrared spe ctroscopy analysis indicated that production of carbohydrate was restrained duri ng the prophase and metaphase decomposition, production of carbonate was acclera ted during the metaphase decomposition, and fatty chain, methyl and methylene we re increased greatly during the whole phase of decomposition. Above conclusions showed that the effects of soil nanometer particles can influence the decomposit ion and conversion of organic matter significantly.