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 t...