Profiles of paddy soils were sampled in Longjing of Jilin Province, Fengqiu of Henan Province, Cixi of Zhejiang Province and Jinxian of Jiangxi Province, which are in different climatic zones. Distribution of organic carbon (OC) andδ¹³C in profiles and organomineral complex of the paddy soils was studied, and structure and functional group composition of humic acid (HA) in different paddy soils was explored with the aid of infrared spectrum (IR). Its aim was to provide some scientific data for reference for the study on organic carbon dynamics and its mechanism. With increasing soil depth in profiles of paddy soils, δ¹³Cof OC increased gradually, and with increasing latitude of the locations of the profiles, δ¹³C of OC increased gradually, too, in the topsoil of the paddy soils. Topsoil OC of paddy soils was mostly concentrated in organomineral complex in the size fraction<10 μm, and their OC abundance was over 50%. With decreasing particlesize, δ¹³C of topsoil complex increased continually, and old OC high in ¹³C natural abundance accumulated in fine particles. In terms of degradation degree of OC in soil complex<10 μm, the four profiles were in a decreasing order of Fengqiu > Cixi > Jinxian > Longjing. Structure of the HA differed slightly between paddy soils. Compared to paddy soils sampled in Cixi and Jinxian, paddy soils sampled in Fengqiu and Longjing contained HA high in C=O groups, and in oxidation, aromatization and polymerization degrees.