It is revealed by our studies that the Jiaoling red earth in the hilly area, northeastern Guangdong, South China, developed in the last interglacial period and belongs to silty clay in terms of lithology. Meanwhile, the red earth’s finegrained clay content 1215%～24.64% (average 18.46％)，Mz5.91Φ～753Φ(672Φ) and the foursegment distribution of cumulative probability curve is roughly consistent with the threepeak distribution of frequency curve for each sample. The primary oxides of major elements are mainly SiO2, Al2O3and TFe2O3(Fe2O3＋FeO), of which the contents are 50.10%～53.14％(51.36%)，23.07%～24.44％(24.00%), 10.18%～11.40％(10.77%) , respectively, whereas the CaO, Na2O, MgO and K2O contents are all below 1%. Moreover, The approximative fine silt distribution of grain size and the desilicification—allitization phenomenon indicating a strong chemical weathering and eluviation. In addtition, the Si/Al ratios of most red earth horizons indicate a less intensive allitization. A thorough comparison of the content of grains smaller than 2μm or 1μm, Si/Al ratio, and CIA between Jiaoling red earth and mordern latosolic red soil, and laterite in some of China’s north tropical and south subtropical zones reveals that the red earth developed in a climatic environment that is more warm—humid than that of the present south subtropical zone, and similar to that of the north margin of the present tropical zone. Such a viewpoint is roughly consistent with predecessors' conclusion on the paleoecology indicated by the Ailuropoda—Stegodon fauna during that period. Therefore, we conclude that the last interglacial northeastern Guangdong and even the full extent of South China were in a climatic environment similar to that of the north margin of present tropical zone, and the boundary between the tropical and subtropical zones experienced a northward migration of at least 3 degrees of latitude.