Every Japanese steel enterprise is currently operated at so high production rate that reliable refractory materials, which exhibit excellent and stable durability in hot service, are requested fiercely. To secure sufficient stability, careful study and analysis are essential on the influence of mixing formulation, installing condition and environment to the material performance. However, many experiments and, therefore, a large amount of time and cost are requested for such study and development if it is carried out by means of conventional methods. This paper reports an effective method to develop refractory materials of less variability. So-called "robust design", a tool in "Taguchi methods" or quality engineering, is employed effectively to attain excellent stability in the materials. In most case, variations of the material properties are caused by uncontrollable factors in manufacturing. In robust design, the stability is pursued not by controlling these uncontrollable factors but by minimizing their influence to the variability by means of adjusting the controllable factors. This paper introduces a concrete application example of robust design, in which it is confirmed that robust design is useful as a development tool to provide the stable properties to refractory materials and also that control factors and noise factors have to be carefully selected to succeed in the material design.