The composition and properties of humus in the cultivated red earth is influenced to a great extent by farming measures. Especially, under the conditions of organic manuring and rice planting, the composition of humus may go beyond the influence of geographical zonality and degree of humification can be increased significantly, the valne of ΔlogK can be decreased gradually and the ratio of humic acid to fulvic acid may be more than 1. The ratio of H.A./F.A. in paddy soil derived from the red earth with higher fertility is 1.4, that in paddy soil with medium fertility is about 0.5 and that in paddy soil newly reclaimed is 0.2-0.3 which is similar to that in virgin red earth;and the ratio in dry farming red earth with higher fertility is about 0.9. All these mentioned above showed the characteristics of soil humus under cultivation and manuring of high yield rice, and the ratio of H.A./F.A. might be considered as the.main index of fertility of red earth. This study also showed that the variation of contents and properties of humus of red earth was restricted in the surface soil, and with the duration of cultivation it was gradually influenced in the other horizons of the profile.Because of excess of water and lack of oxygen, the composition of humic acid in paddy soils derived from red earth with lower and medium fertility is simpler than that in upland soils, though the humus in these soils is accumulated faster. After a long period of rice planting, the rotation of rice and upland crops can regenerate the soil organic matter and improve its quality, being conducive to the improvement.