The Aconcagua River basin, located in central Chile, is one of the most important agricultural areas in the country. Chile is the first among the producers of copper in the world; and several important copper mining industries are located in agricultural areas of the basin. Copper is an essential micronutrient to all organisms, but it can be toxic to plants and soil organisms at specific elevated concentrations. In contrast, copper toxicity to humans is very uncommon due to their effective homeostatic defense mechanisms against copper. In spite of the environmental importance of copper, surprisingly few data are available on its distribution and biotoxicity in agricultural soils in the Aconcagua River basin. The objective of the present study was to evaluate the ecotoxicological quality of some agricultural soils located in the proximity of copper mining industries in the basin. For this purpose we have performed tests with earthworm Eisenia fetida, which is considered to be representative of soil fauna. The protocols for earthworm toxicity tests have been developed and standardized by the Organisation for Economic Cooperation and Development (OECD, 2000). We determined physico-chemical characteristics of the soils (organic matter content, pH, and texture), copper concentrations (total and extractable in 0.1 M KNO₃), activity of free cupric ion (Cu²⁺) in the solution of 0.1 M KNO₃, and acute and chronic toxicity with the earthworms. Total copper concentrations in the soils varied between 65 mg/kg (San Felipe) and 1565 mg/kg (Chagres). Concentrations of extractable copper and free Cu²⁺ were linearly correlated with the total soil copper. Based on Electron Probe MicroAnalysis (EPMA), copper in the studied soils were present as sulfides and adsorbed on iron oxides. These minerals have low solubility and extractable copper represented only very small fraction (<0.5%) of the total copper. Free Cu²⁺, in turn, represented only very small fraction (<0.5%) of the extractable copper. This suggests that more than 99.5% of the extractable copper is bound to organic ligands. Although these copper concentrations did not induce acute toxicity in the earthworms, they did induce chronic toxicity affecting earthworm reproduction. We have observed decrease in production of cocoons with increase in copper concentration in the soils. The greatest effect was observed in the soil collected in the proximity of the Chagres smelter, with 84% of reduction in production of cocoons. These results suggest that the studied soils have a very diverse ecotoxicological quality that reflects the impact of copper mining activities in the basin. We believe that organism toxicity testing provide a more reliable and accurate method for determining acceptable concentrations of copper in the soils in comparison to the total copper contents and chemical extraction techniques that have been used historically. Keywords: Agricultural soils, Chile, copper, organism toxicity testing, soil ecotoxicological quality, earthworm Eisenia fetida. Acknowledgment: This study has been funded by the Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) project No. 1050403.