This study quantified the soil and carbon fluxes caused by water erosion within the sloping uplands of the Mekong River basin, a river system carrying one of the greatest worldwide amounts of sediment to the ocean. Losses of sediment and soil organic carbon (SOC) (including black carbon, BC) were evaluated within an agricultural catchment of 62 ha with steep slopes, on a tributary of the Mekong river, at nested scales of micro-plot (1 m2), micro-catchment (0.6 ha) and catchment (62 ha), in an attempt to explain the processes involved in water erosion. In 2002, carbon erosion occurred during 35 rainfall events amounting to 1023 mm of an annual total of 1651 mm. Water erosion removed annually 14.1 t ha-1 of sediment and 0.69 t ha-1 of SOC from the study site. This is equivalent to 7.75 and 0.51 Pg yr-1, respectively, for the uplands of the Mekong basin as a whole. When compared to the bulk soil, the eroded soil material was enriched in SOC and BC by factors of 2.3 and 1.4, respectively. The annual yields of soil material from the micro-catchment were 3 times lower for sediment and 6 times lower for SOC than those from the micro-plots. From the micro-plots to the catchment, the yields decreased by a factor of 25 for sediment and 59 for SOC. Although a considerable amount of soil material is detached from its original site by water erosion, most of this material is redistributed within the landscapes, being deposited in places acting as sinks, such as hillslopes, and valley bottoms where BC is preferentially deposited. The loads from the catchment of 0.56 t ha-1 yr-1 for sediment and 0.016 t ha-1 yr-1 for SOC were considerable, corresponding to 0.31 Pg of sediment and 0.01 Pg of SOC for the Mekong basin uplands as a whole. These results on the selective water erosion of soil material, SOC and BC on sloping lands of Southeast Asia allow the source and sink functions of the sloping lands of tropical landscapes to be better understood.