The characteristics of electric charge and molecular weight distribution, oxidation-reduction regimes, e.g. Eh and amounts of organic reducing substances produced by milk vetch during anaerobic decomposition process, were studied by using electrochemical methods. Interaction between soils and organic reducing substances was also observed. The results indicate that the organic reducing substances were mainly the organic compounds with negative and amphoteric charges, which were distributed in two groups at anodic peak potentials of 0.25 and 0.69 volt in differential pulse voltammograms, respectively. Their apparent molecular weights are all less than 700 daltons, in which those active in oxidation-reducion reaction were distributed in the fraction with apparent molecular weight less than 200 daltons. The organic reduction substances can be oxidized by manganese oxides in their interaction with soils. The characteristics of electric charge and molecular weight distribution, oxidation-reduction regimes, eg Eh and amounts of organic reducing substances produced by milk vetch during anaerobic decomposition process, were studied by using electrochemical methods. Interaction between soils and organic reducing substances was also observed. The results indicate that the organic compounds with negative and amphoteric charges, which were distributed in two groups at anodic peak potentials of 0.25 and 0.69 volt in differential pulse voltammograms, respectively. Their apparent molecular weights are all less than 700 daltons, among which those active in oxidation-reducion reaction were distributed in the fraction with apparent molecular weight less than 200 daltons. The organic reduction substances can be oxidized by manganese oxides in their interaction with soils.