This paper investigates the effects of using Ground Granulated Blast Furnace Slag (GGBFS), Lead Slag (LS) and Zinc Slag (ZS) as replacement for sand on the strength of concrete. Compressive strength, flexural strength, water absorption and density were tested at 14, 28 and 56 days. In this study, a total of 40 concrete samples, including Pozzolanic Portland Cement (PPC), GGBFS, LS and ZS concretes, were produced with a water-to-cement ratio of 0.4, cement content of $400kg/m^3$ and slag/sand replacement ratio of 30%. A superplasticizer was used in concrete at a proportion of 1.5% per weight of cement. The results show that the type of slag affects the mechanical properties of concrete. Compressive strength increased when GGBFS was used but decreased or remained unchanged when ZS or LS, respectively, were used as sand replacements in concrete. The results also demonstrated that the flexural strength of control concrete was higher than that of other mixtures. Dry density increased and water absorption decreased with the use of slags in concrete. In general, it can be concluded that the use of GGBFS and lead slag as fine aggregates in concrete is technically possible and useful in some cases, whereas the use of zinc slag has a negative effect on concrete.