The USLE model was evaluated to estimate water erosion in an Alfisol located in San Pedro, Metropolitan Region of Chile. Values of erosivity (R) obtained by using the Arnoldus approximation (MFI) and equations proposed by the Institute for Nature Conservation (ICONA) in Spain were adapted to the conditions in Chile. For the evaluation of soil loss, data were used for each precipitation event causing erosion during the period 1996-2000, obtained by measurements on experimental plots with treatments of subsoiling, infiltration trenches and natural prairie. They were compared with estimated values of erosion in terms of basic statistics and indices based on variance and regression. In the descriptive and comparative analysis of the selected equations, it was determined that soil losses estimated with USLE using the equation of rainfall erosivity by ICONA provided soil loss values which were well-adjusted to the values recorded in Chile, compared to erosivity calculated by the Arnoldus approximation (MFI) that overestimated the soil loss values. According to the results or estimates in this study it was concluded that the USLE model was capable of detecting the trend of the data, and resulted in estimates consistent with the pattern observed in the field data.