This paper will discuss that copper slag, a by-product of copper production, contains large amounts of iron oxide and silicate. It is chemically stable and its physical properties are similar to that of natural sand. The physical and chemical properties of copper slag were investigated. Copper slag, in amounts of 20, 40, 60, 80, and 100 percent, was substituted for fine aggregate in cement mortar and concrete. The fineness modulus of the combination of copper slag and fine aggregate was roughly 2.6, the optimum fineness modulus for concrete mix design. At this value, workability was found to be satisfactory with minimal bleeding. Addition of copper slag also improved the strength of the concrete. When the substitutional amounts exceeded 80 percent, lower strengths were obtained, possibly due to the formation of ettringite. It was also found that the effect of copper slag on long term strength development was also dependent on the amount used and its fineness. It was concluded that copper slag could be used as a fine sand substitute for ordinary reinforced concrete.