By investing soil forming environment, profile morphological characteristics and physico-chemical properties of 12 typical soil profiles derived from Quaternary red clay in eastern Hunan Province, this paper examined the diagnostic horizon and diagnostic characteristics of these soils in Chinese Soil Taxonomy (CST) and defined their types of soil family and soil series. The results showed that there are 10 diagnostic horizons and characteristics such as Ochric epipedon, Umbric epipedon, LAC-ferric horizon, Argic horizon, Plinthic horizon in the 12 soil profiles. According to CST, they belong to 3 orders such as Argosols, Ferrosols, and Cambosols; 3 suborders like Udic Argosols, Udic Ferrosols and Udic Cambosols; 3 groups as Hapli-Udic Ferrosols, Ali-Udic Argosols and Ali-Udic Cambosols; and 6 subgroups as Rhodic Hapli-Udic Ferrosols, Trunic Hapli-Udic Ferrosols, Plinthic Hapli-Udic Ferrosols, etc. In addition, according to the Classification Standards for Soil Family and Soil series of CST, 9 soil families and 12 soil series were defined for the 12 profiles. The result showed that under the impact of subtropical monsoon climate, many soil profiles are ferrallitic. Due to the intensive leaching, plinthic horizon has been formed. However, no appropriate position can be found for such characteristics in CST, therefore, it suggested that a mew subgroup of Plinthic Ali-Udic Agrosols reflecting related characteristics should be added in CST.