In order to learn how the organic manure application influences the structural characteristics of humic acids in soils, a comparative study was initiated by the method of ¹H-NMR spectra of humic acids separated from the soils (brown soil, meadow soil and paddy soil) with and without organic manure applications (pig manure, corn stalk and rice straw) in field and incubation experiments. The results obtained are summarized as follows:In the solvent system of DMSO-d₆, the absorption peaks of ¹H-NMR spectra were 0.8, 1.2, 3.4, 3.7, 4.4, 6.7, 7.2 and 8.1 ppm. The absorption peaks of 0.8 and 1.2ppm were the contribution of-CH₃ and polymethylene chain(-CH₂-)_n in saturated hydrocarbons respectively; the signals of 3.4, 3.7 and 4.4ppm were due to the H connected with the carbons in carbonhydrate (α-CH;and the peaks at 6.7, 7.2 and 8.1ppm were generally assigned to aromatic H and-COOH (Ac-H).In the solvent system of NaOH-d₁, signals at 1.8, 2.1,and 2.4ppm. were found. It was suggested that these arise from protons attached to carbon a to aromatic ring or other unsaturated groups and α-CH or β-CH in indanes and tetralins of the humic acid.Application of organic manures led to the increase in the relative content of aliphatic H (ali-H).However, the methylene chains (n value) became shorter after organic manure application. On the other hand, the content of aromatic protons (Ar-H) and aromaticity (faH) in humic acids decreased because of organic manure application, which resulted in the increase in the ratio of aliphatic H to Ar-H in the humic acids. Results also showed that pig manure (PM) was more effective than corn stalk (CS) or rice straw (RS) in raising the proportion of aliphatic chain hydrocarbons in humic acids. Whereas CS and RS were more effective in increasing the relative content of carbohydrates in humic acids.