Abstract: The effect of organic materials(O.M.)on improving the fertility of red earth-derived paddy soil was monitored for 13 successive years.Result indicated that O.M.markedly increased the amount of Organo- mineral complex in soil and, in varying degree, bettered its quality.The complex quantities of initial soil in decreasing order were:Pig manure(treatment)>Azolla, Green manure,Rice straw >Blank and additional complex quantities were: Pig manure > Azolla > Rice straw>Green manure.However, the additional complex degree of pig manure treatment was the lowest because of its high carbon input and low decomposition in present season.O.M.was benefi- cial to the formation of coarse aggregation and the increase of the enzyme activities, such as cata- lase by 70%- 80%and converzyme by 20%- 40%.Azolla is one of the best organic materials with high efficiency of carbon humification.Azolla mainly bettered nitrogen supply of soil, and rice straw improved potassium and pig manure improved phosphorus and then nitrogen.