The use of copper slag as a replacement for fine aggregate in construction will reduce damage to the environment due to the waste resulting from the copper manufacturing process and help in saving natural resources. In this research, the use of copper slag as a replacement for fine aggregate is investigated. Three slender reinforced concrete columns of 150x150x2500mm were tested for monotonic axial compression load until failure. The concrete mix included ordinary Portland cement, fine aggregate, 10mm coarse aggregate and copper slag. The ratios of copper slag to fine aggregate were 0%, 40% and 80%. Four-8mm diameter high yield steel bars were used as longitudinal reinforcement and 6mm diameter mild steel bars were used as stirrups. Three cubes, 100x100x100mm, three cylinders, 150x300mm, and three prisms, 100x100x500mm, were cast from the same mix of each specimen at the same time. Curing for the specimen and the samples was carried out using wet Hessian cloths for one week and then they were left under room temperature for about five weeks. Test results were judged by longitudinal steel strain, lateral displacement and failure load. The test results so far showed that up to 40% replacement of fine aggregate by copper slag does not have a significant effect on the load carrying capacity of the columns. Increasing the copper slag beyond this ratio accelerates the buckling, which leads to premature (before steel yields) failure load and a larger deflection.