The aim of this study is to design concrete mixes, which is used in cement bricks and walls using recycled rice straw and blast-furnace slag. The studied factors are rice-straw content (3, 6, 9, 12, 15 % related to cement mass) for both rice straw (untreated and treated with NaOH with 1 % concentration). The main results show that; At 28 day, compressive, tensile and flexural-strength ranges of “20.56 – 3.7 and 17.03 – 3.44”, “2.65 – 1.17 and 2.52 – 1.03” and “6.49 – 1.66 and 3.04 – 0.84” MPa were obtained by using concrete mix with rice straw of 3 – 15 % for treated and untreated rice-straw respectively. Meanwhile, for concrete mix without rice straw (control) the strength values of 32.1, 2.78 and 5.9 MPa were obtained. The maximum absorption and porosity of 33.54 and 32.05 % respectively, were obtained for concrete specimens made by using untreated rice-straw of 15 %. Meanwhile, the minimum absorption and porosity values of 5.71 and 13.47 % respectively, were obtained by using concrete mix without rice straw. The real-density ranges of 1961 – 1444 and 1816 –
1371 kg/m3 were obtained by using concrete specimens made with rice straw content of 3 – 15 % for treated and untreated rice-straw ,respectively. Meanwhile, for concrete mix made without rice straw (control), the density is about 2243 kg/m3. The costs of 1000 brick unites were 550, 370, 360, 350, 340 and 330 L.E. for bricks containing 0, 3, 6, 9, 12 and 15 % rice straw, respectively.