Particle-size distribution of five typical profiles of Quaternary red clay in Yichang and Xianning, Hubei Province, and Changde, Changsha and Zhuzhou, Hunan Province, the middle reaches of the Yangtze River, was analyzed to study origin of the Quaternary red clay and its implications for evolution of the paleo-environment in South China. Results indicate that all the profiles demonstrate obvious dualistic structure in particle-size composition, e.g. in the upper part of the profile (0～320 cm of the Yichang profile, 0～220 cm of the Xianning profile, 0～270 cm of the Changde profile, 0～280 cm of the Changsha profile, and 0～150 cm of the Zhuzhou profile), the clay is fine and uniform in particle size and low in content of sands, mostly <1%, and relative high in content of coarse silt or basic component of aeolian dust fraction, accounting for 34.38%, 32.29%, 32.48%, 31.69% and 31.86% on average, respectively. Moreover, the particle-size distribution frequency graphs of the red clay samples are similar to those of the Quaternary red clay in Xuancheng, Anhui Province, and also show some inherited patterns from the Xiashu loess in Zhenjiang, Jiangsu Province. All the above reflect the aeolian characteristics of the red clay in the upper parts. However, the lower parts of the profiles is significantly different from the upper in particle-size composition. They often have gravels and a relatively high content of sands, showing a significant vertical variation of different particle-size fractions along the file. Furthermore, the files are also significantly different from those of the Quaternary red clay in Xuancheng, Anhui Province, and the Xiashu loess in Zhenjiang, Jiangsu Province, in particle-size frequency graph, demonstrating diluvial or alluvial properties. The dualistic structure of the Quaternary red clay in the middle reaches of the Yangtze River manifests variability and complexity of the paleo-environment in the study area. After the red clay formed in the early stage of the Quaternary period, it was often exposed to the impact of interglacial hot and humid climates and flowing water, while in the later stage of the period, the red clay was subjected more to aeolian deposition, and maintains its aeolian characteristics though it has experienced strong in situ weathering during the post-depositional processes.