The composition of the humus of paddy soils developed under four different bioclimatic zones was studied. It is compared with the humus composition of corresponding soils under dry farming or/and under natural vegetation. Results obtained showed that both the humic acid/fulvic acid ratio and the degree of humification of humic acid decrease regularly in the following order: brown earth zone-yellow brown earth zone-red soil zone and lateritic soil zone. In the same bio-climatic zone, the humus of paddy soils is characterized with a higher humic acid/fulvic acid ratio and a lower degree of humification as compared with other soils. It was suggested that the water-logged condition of paddy soils favours the accumulation of humic acid but retards it form further condensation.