Because of their fertility and ease of cultivation loessial soils have been in agricultural use for ages. These soils are, however, very susceptible to water erosion processes. Even small inclinations of few degrees may result in medium to large sheet erosion of loessial soil. Additionally, an inappropriate soil tillage intensifies the soil erosion. There is an urgent need to obtain reliable quantitative data of soil erosion for agricultural areas to choose an effective method of soil conservation. The 137Cs technique seems to be a valuable to study soil erosion and deposition. This isotope has been present in the environment since the beginning of nuclear weapon testing and nowadays 137Cs is a part of many ecosystems. The 137Cs method overcomes many limitations of the traditional methods to measure soil erosion. In this paper we present the use of measurements of 137Cs activity in soil as a tool to investigate the soil erosion process in the loess agricultural field. The study area is a small loess catchment located on the Proboszczowicki tableland (near Ujazd village). Results presented in this paper were obtained on five valley profiles collected in the study area. The soil samples were measured, after drying, by the high-resolution gamma spectrometry to determine their radioactivity. The study area was contaminated by 137Cs from Chernobyl accident. This study is to evaluate the soil erosion as well as accumulation for small agricultural loess catchment. Moreover the aspect related to the model for calculation of soil erosion from the 137Cs activity data are discused. This method allows to evaluate soil erosion for medium-term. Finally, the influence of 137Cs from Chernobyl on the calculation of soil erosion is discussed.