In this study, the use of steel slag as fine and/or coarse aggregate in concrete is investigated. For this purpose, 12 different concrete mixtures with different water/cement ratios of 0.40, 0.55 and 0.70 which include steel slag aggregate as fine and/or coarse aggregate are prepared. Compressive strength, split tensile strength, flexural strength, freeze-thaw resistance and water penetration depth of concrete mixtures containing steel slag aggregate are examined in comparison with concrete mixtures prepared by using crushed limestone aggregate. Eventually, concrete mixtures containing coarse steel slag show better performance than concrete mixtures containing limestone aggregate. Concrete mixtures containing fine steel slag show worse performance in comparison with concrete mixtures containing limestone aggregate.