The target of this research is to design concrete mixes which used in cement bricks and walls by recycling rice straw and blast-furnace slag. The investigated factors are rice-straw percentages (3, 6, 9, 12, 15 % related to cement mass) under different treatment of rice straw (untreated and treated with NaOH with 1 % concentration). The results mentioned 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, the compressive, tensile and flexural-strengths of 32.1, 2.78 and 5.9 MPa were obtained by using concrete mix without rice straw (control),the maximum absorption and porosity of 33.54 and 32.05 % were obtained by using untreated rice-straw of 15 % content. Meanwhile, the minimum absorption and porosity 5.71 and 13.47 % were obtained by using concrete mix without rice straw. at 28 day, real-density ranges 1961 – 1444 and 1816 – 1371 kg/m3 were obtained by using concrete mix with rice straw of 3 – 15 % for treated and untreated rice-straw respectively. Meanwhile, the real density of 2243 kg/m3 was obtained by using concrete mix without rice straw (control),the costs of 1000-bricks were 550, 370, 360, 350, 340 and 330 for 0, 3, 6, 9, 12 and 15 % rice straw respectively.