Abstract: Stratigraphic sequence and constant elements were studied in Mituosi’s loess profile，Yun County，Hubei Province，China. And optically stimulated luminescence（OSL）was carried out on dating the loess sediments. The aim is to discuss the chemical weathering characteristics and the palaeoenvironmental change based on comprehensive approaches，such as Chemical Index of Alteration（CIA），A-CN-K diagram，Na/K and Fe/Mg. Results showed that the major composition of Mituosi’s loess section was made up with SiO₂ and Al₂O₃. Na₂O，MgO，CaO were performed leaching in the profile，while Fe₂O₃，K₂O and Al₂O₃ were enriched. Moreover these elements behaved leaching or enriching more intensely in the palaeosol. The leaching of Na，Mg and Ca is due to the weathering of plagioclase and pyroxene. While Fe and Al’s relative enrichment is because of leaching of other elements. The K enrichment is likely to be its ion adsorpted by relevant clays. These elements’geochemical variations could reflect the pedogenic modification of loess in Mituosi. The CIA（65.41）and A-CN-K diagram showed the profile experienced the primary chemical weathering processes in which Ca，Na loss was serious，but almost no leaching of K. And it was transited to middle stage of chemical weathering. The weathering products mainly are montmorillonite and illite. It has not reac- hed kaolinite and gibbsite-based degree of weathering .The CIA，Na/K and Fe/Mg’s curves all indicated the weathering was from weak to strong degrees and then weakened，which from Malan loess to palaeosol then to Holoncene loess. This information revealed the palaeoenvironment，especially the palaeoclimate change since the late Pleistocene. The climate was characterized by cold and dry climate at about the late Pleistocene 18 000-11 500 a BP；Then that came to the Holocene，it was becoming warm. And the Holocene warm period was during 8 500-3 100 a BP，after about 3 100 a BP. The climate turned cool again. All above indicated the climate was“cold-dry→warm→ warm-wet→cool-dry”. Meanwhile the climatic cold fluctuation events at about 6 000-5 000 a BP. have been recorded and responded by Mituosi’s loess.

Key words: loess, chemical weathering, climate change, Mituosi, the upper reaches of the Hanjiang River