In coal-fired thermal power plants, the waste/by product deposited under the combustion boiler in the size of micron (μm) occurred during combustion and it is called as “bottom ash”. The bottom ash that generally shows a puzzolanic feature due to its composition containing silica and alumina is also used as an additive material in mortar or concrete. These two types of industrial wastes/by products damage the natural environment and lead to economic losses because of their storage and/or disposal. Use of these wastes in different products and industries can likely contribute to the production of sustainable materials and provide important benefits environmentally and economically. In this study, it is aimed to investigate the effects of the blast furnace slag and the bottom ash on mechanical properties of concrete, substituting these wastes in specific proportions instead of sand used as the fine aggregate in the conventional concrete production. This study has particularly focused on the stress-strain behavior, modulus of elasticity, toughness and compressive strength of finally the change in concrete. In this study, a four-stage experimental program has been followed. In the first stage, a number of experiments that consist of the characterization of all materials to be used have been applied. In the second stage, the composition design of the standard concrete has been prepared using the standard fine aggregate (river sand). In the third stage, the blast furnace slag and the bottom ash have separately been replaced with the fine aggregate in concrete at the percentages of 25, 50, 75, and 100. In the fourth stage, finally, mechanical properties of specimens have been determined after7 and 28 days standard water cure. Consequently, the effect of the use of some industrial wastes/by-products (i.e., granulated blast furnace slag and bottom ash) in concrete as the fine aggregate on mechanical properties of concrete have been investigated.