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Use of the fallout radionuclide cesium-137 (137Cs) as a tracer has been widely employed for assessment of soil losses and dating of deposited sediment; however, few studies have been conducted in karst environments using this technique. In this study, the 137Cs technique was employed to assess sediment deposition rates in a depression in a small catchment of southwest China. Information derived from the 137Cs measurement of sediment samples collected from a depression in a small catchment in southwest China was used to estimate the sediment deposition rate since 1963, and the rate of soil erosion in the study catchment was also discussed. The results presented in this paper indicated that the depression acted as a sink of soils being eroded from the upland slopes. The mean sediment deposition rate and specific sediment yield of the study depression since 1963 were estimated to be 0.37 cm y-1 (0.15 in yr-1) and 50.2 t km-2 y-1 (0.184 tn ac-1 yr-1), respectively. Analysis of the topographic characteristics of the catchment revealed that the rate of soil redistribution of the catchment was very close to the sediment deposition rate of the depression because no significant sediment accumulation occurred upstream of the depression and in the meantime, very few sediments drained out through the sinkhole with the runoff. Therefore, it was inferred that the rate of soil redistribution in the study area was 55.8 t km-2 y-1 (0.205 tn ac-1 yr-1). Overall, the results revealed that there was a low background rate of soil loss in the karst mountain area suffering from severe land desertification in Southwest China. Furthermore, the results illuminated the potential for use of the 137Cs technique to evaluate the sediment deposition and soil erosion rates in karst areas of southwest China, where limited information regarding soil erosion and sedimentation exists. [ABSTRACT FROM AUTHOR]