Abstract: The purpose of this research is to know the specification and character of iron casting waste as a substitute material of coarse aggregate on concrete and to know the value of bending strength of concrete in producing higher quality than regular concrete. This research method is the quantitative method through experimental empirical design. Research in the form of observation and sampling from iron casting waste in PT. Barawaja Makassar. This study was conducted at the laboratory of Universitas Hasanuddin (UNHAS) Makassar. Laboratory tests of aggregate characteristics consist of, specific gravity, absorption, filter analysis, moisture content, volume weight, mud content organic content and wear. Concrete mix design method in this research use DOE method. Tests were performed on the bending of concrete beams and data analysis of concrete test results in graphical form. Iron slag variation as a substitute for some aggregate with levels of 0, 25, 50, 75 and 100% of total aggregate weight. Test results and analysis have been made that iron slag as a substitute agent of coarse aggregate tends to meet all the standard specification requirements as a coarse aggregate. Bending strength of concrete, also increased of iron casting waste 25 and 50%. The highest flexural strength value occurred at 28 days with a value of 5.840 MPa. Added iron casting waste 50% increased 39.71% compared to regular concrete. However, there was a decrease in 75 and 100% iron foundry waste substitution. The use of iron waste as a rough aggregate added material can produce high concrete when compared to regular concrete.