In Tunisia, the semi-arid domain is threatened by soil erosion risk due to its aggressive Mediterranean climate, hilly terrain, and inadequate reckless human intervention. In this context, our study aimed to quantify soil erosion and deposition in cultivated and uncultivated fields in Lakhmess watershed (northwestern Tunisia) using the (137Cs) technique. The soil samples were collected based on the transect approach, and the reference site was identified as an old graveyard. Soil erosion and deposition rate were estimated using the FRN’S conversion models described by (Walling et al., 2003; Quine and Walling, 1991). The proportional model (PM), the Mass Balance Model I, and the Mass Balance Model II were used for the cultivated field, and the Profile Distribution Model (PDM) and the Diffusion and Migration Model (DDM) were applied for the uncultivated field. The 137Cs inventory in the reference site was 1458 Bq m−2, with a coefficient of variation (CV) of 15%. The mean net erosion rate for the cultivated field was 35.43 t h−1 yr.−1 for PM model, 73.55 t h−1 yr.−1 for MBM I, and 36.96 t h−1 yr.−1 for MBM II. The mean soil erosion rate for the uncultivated field was 0.66 t h−1 yr.−1 using the PDM model and 3.64 t h−1 yr.−1 using DDM model. The difference of the mean soil erosion rate estimated by different models in each field is related to characteristics of the model used for soil loss estimation. Findings of this study will help the land use planners to plan effective conservation management practices in the study fields.