To study pedogenetic process and taxonomy of red clay in Beijing, six red clay profiles developed from granites and limestones were selected as samples for analysis of soil profile morphology, soil physical and chemical properties and soil mineral composition. Results show that argillan existed on the surface of soil ped of all the soil profiles, no lime reaction was observed throughout the profiles, and the soils were high in Fed/Fet and low in Feo/Fed. The red clay soil originated from limestones was finer in texture, higher in free iron, redder in color and higher in aggregation degree of the ped, while those from granites was lower in aggregation degree of the ped because of its higher content of sands of hard-to-weather quartz. During the pedogenetic processes of the soils, intensive argillation and ferruginization occurred presumably under hot and humid paleoclimate. However, with time elapsing, the red clays in the area have now become slightly alkaline or neutral in pH, dominated with Ca² in exchangeable base and high in base saturation, as a result of modern loess precipitation and consequent base complication. According to the principles and methods of Chinese Soil Taxonomy (3rd edition), the six red clay profiles should be sorted into four different subgroups of Argosols.