The fallout radionuclide cesium-137 (¹³⁷Cs) has been widely employed as a tracer for assessment of soil loss from thick uniform soils; however, few studies have been conducted on thin stony soils on slopes underlain by carbonate rocks which are widely distributed in karst areas. Information derived from ¹³⁷Cs measurement of soil samples collected along a carbonate rock slope with thin stony soil where neither soil erosion nor deposition occurred was used to investigate the characteristics of ¹³⁷Cs redistribution in a karst area of Southwest China. The results indicated that the ¹³⁷Cs inventories of the surface soil on the slope studied were much lower than that of the local ¹³⁷Cs reference inventory and the ¹³⁷Cs activities were much higher than those on slopes with thick uniform soils. The spatial distribution of ¹³⁷Cs inventories was characterized by considerable variation. The high ¹³⁷Cs depletion in the stony soil of the slope studied was mainly because a considerable proportion of the fallout input of ¹³⁷Cs could be lost with runoff and the dissolution of carbonate particles in the soil promoted the loss of ¹³⁷Cs. These demonstrated that the rates of soil loss could not be estimated from the degree of depletion of the ¹³⁷Cs inventory relative to the local reference inventory for the thin stony soil of the rocky slope underlain by carbonate rocks in the study area in the way that has been widely used in areas with thick uniform soils.