Chemical composition and structure of humic acids extracted from composted corn stalk residue(CSR) were studied with the aid of Fourier transform infrared (FTIR) spectroscopy, ¹H and ¹³C nuclear magnetic resonance(¹H-NMR, ¹³C-NMR) spectroscopy and chemical analysis.The carbons in Humic acid from composted CSR (CCSR HA) can be mainly divided into three groups: aliphatic-C, aromatic-C and carbonyl-C, accounting for 59.62%, 26.94% and 13.44% of the total C, respectively.The major functional groups in the CCSR HA include hydroxyl, alkyl, carboxyl, amide, benzene ring, methoxyl, carbonyl and carbohydrate, with residual lignins being their skeleton and carbohydrates, and long-chain aliphat ic structural groups their basic composition units.CCSA HA is of the Rp type of humic acids.In uncomposted corn stalks per se humic acids (OCSR HA) can be found and it is somewhat different from CCSR HA in composition of funct ional groups.The latter is relatively lower in methyl, methylene, ether and phenol hydroxyl but higher in amide, free carboxyl, methoxyl and carbohydrate.Aromaticity of CCSR HA is 29 97, and significantly lower than that, 42.19, of OCSR, but the capacity of CCSR HA combining with inorganic matters becomes stronger.As far as variation of the elemental composition is concerned, the contents of C and H are lower and the contents of N and O are higher in CCSR HA as compared to what is in OCSR HA.Compared with soil HA, CCSR HA is significantly lower in aromat icity, but much higher in content of sugar-like components, which are not present as free carbohydrate, and instead are incorporated into structures such as hydrolyzable lignins.CCSR HA is also comparatively lower in content of carboxyl groups, which exist in different forms.