Land use and geomorphology of hillslope play important roles in influencing soil water erosion which is the primary factor for the depletion or restoration of soil organic carbon stock (SOCS). Reliable information on the impact of erosion/deposition dynamics on SOCS is required for effective accounting of the carbon flux that indirectly influences management of climatic change. The main objectives of this study were to determine soil redistribution on the basis of the variation of 137Cs radionuclide activity under different land uses and hillslope components in a mountainous catchment of western Iran. Also, the relationship between soil erosion and deposition rates, using 137Cs inventory-conversion models and storage and loss of soil organic carbon stocks was examined. To do this, 137Cs activity and SOCS were measured in thirty-two sample sites from different hillslope components in cultivated and forested areas. The simplified mass-balance model and diffusion and migration model estimated very high erosion rates of 6.43 and 40.3 t ha− 1 yr− 1 in the shoulder component of forest and cultivated areas, respectively. In both disturbed (cultivated) and undisturbed (forested) soils, positive and statistically significant relationships were found between the SOCS and 137Cs inventory. Consequently, 137Cs could be used directly for quantifying dynamics of SOC in soil redistribution relationship as affected by soil erosion. Statistical analyses also indicated that the 137Cs activity and inventory, SOCS and erosion/deposition were significantly affected by landform components and land use types.