Forest fires have become a major threat to some soils in the Chilean Patagonia. More than 36,000 ha of predominantly native forest have been burned in the last four decades in the Serrano River basin, most of them in the Torres del Paine National Park, a world biosphere reserve. A study was conducted to evaluate the effects of forest fires and water erosion on the soil organic carbon (SOC) in the Serrano River basin. A total of 17 sites were sampled, three major soil types were found (Dystric Cambisols, Lithosols, and Luvic Phaeozems), and three main forest fires were identified. Soils were sampled at two depths and analyzed to determine their texture, SOC, cation exchange capacity, total N, P, and K, and aggregate stability. Soil erosion rates were estimated using the Water Erosion Prediction Project (WEPP) model with actual soil, vegetation, and weather data. The SOC content was the main significant difference between samples at depths of 0.2 and 0.4 m, at both burned and unburned sites. The 0.2-m-depth samples had an average SOC of 5.1 %, compared to 3.2 % for the 0.4-m-depth samples. The nutrient contents and CEC were also higher in the upper layer. The burned and unburned sites were not found to be different in their SOC contents or other soil properties, with the exception of P availability. As a result of the bareness of their soil, the burned sites had the highest water erosion rates (9.3 t ha(-1) year(-1)) and SOC losses (0.5 t ha(-1) year(-1)).