The Badain Jaran Desert（巴丹吉林沙漠）, located in the western part of InnerMongolia, is the third largest desert in China. A variety of sediments and sedimentary rocks in the vicinity of the Badain Jaran Desert ranging from sediments of the Ruoshui River (弱水河) fan to slightly consolidated Permian shales, Cretaceous sandstones and conglomerates and ancient rocks of the Gobi Altai mountains (戈壁阿尔泰山) have been suggested to be possible sand sources for the dunes of the desert in previous years. According to a granulometric survey of aeolian sands, there is evidence for a slight but distinct aeolian fining towards the southeast within the desert which is in agreement with the SW-NE alignment of the transverse dune ridges and slope faces pointing towards the southeast. Therefore the alluvial fan of the Ruo Shui River in the northwest of the desert has to be considered as the most probable source area for the aeolian sands of the Badain Jaran Desert. In the northwestern part of the desert the aeolian bedforms cover alluvial sediments of an older ruoshui fan generation. Results of thermoluminescence dating of such sediments range between approximately 190 ka and 100 ka BP which represent maximum ages due to uncertainties related to the dating of probably incompletely bleached sediments and the estimation of the palaeo-mean water content of the sediments and due to the dating of deposits which were accumulated prior to the onset of aeolian processes in this part of the desert. Three additional datings of aeolian sands yielded ages of approximately 133, 66 and 22 ka BP respectively which represent minimum ages for the onset of aeolian processes in the related north-western part of the Badain Jaran Desert. The dunes of the desert are between 200 and 300 m high in average but attain elevations up to 450 m in the southeastern part occasionally. A steep inselberg relief which is covered by the aeolian bedforms was proposed by several authors to explain the extraordinary dimensions (Petrov 1966; Zhu et al., 1986; Yang, 1991; J kel, 1996). As a result of this study, the part of the desert under consideration was found to be underlain by a platform topography of Cretaceous fanglomerates and sandstones which rest generally more or less horizontally. This platform morphology is pronounced in the southeastern vicinity of the desert but obviously extents further to the north under the dunes of the desert. Therefore it is assumed now that the high dunes of the Badain Jaran Desert are the result of the interaction of different regional climatic and geomorphologic factors rather than covering a steep inselberg relief. The verification of the alluvial fan of the Ruoshui River as the main source area of the Badain Jaran Desert emphasizes the environmental importance of this region. During the Holocene, sand supply from the alluvial fan was probably hampered to some degree by oasis vegetation along river courses. At present, the riverine forests are greatly endangered by water withdrawal for irrigation purposes in the Hexi Corridor (河西走廊). Therefore, a threatening significant increase in sand mobilization has to be avoided by maintaining a sufficient river discharge to preserve the locally dense vegetation along the Ruoshui River acting as a natural sand trap.