To enhance product added-value, there is an increasing trend recently to print wood grain patterns or give texture to building materials and industrial products by surface treatment. Surface treatment is not only applied for decorative purposes but it also serves practical purposes such as hiding surface damage and uneven coating invisible. The methods of designing wood grain and texture on surface are presently limited to the following three: 1) Copying the surface of natural objects, 2) designed by professional designers, and 3) outputting algorithms from computer. The first method by copy can create natural design but is not unique. The second method is difficult when there is a need to create various designs since this method requires considerable time and cost. And the last method by computer is able to output consistent designs but can not generate design expressing natural impression. The goal of this study was to develop a system for designing unique, natural, and diverse product surface textures using computer algorithms, To realize these three features, the system was designed to apply "fractal" and "1/f fluctuation", which are inherent in the natural world. A basic form of texture is constructed as "fractal", which can generate endless varieties of form, and "1/f fluctuation" is added to the basic texture to provide a natural feel. The system allows everyone from the layman to experts to design such textures easily using a developed user-intuitive interface, and check texture form in real time. From this system, a variety of textures, from consistent design to natural design, can be generated from different patterns of parameters such as "fractal" and "1/f fluctuation".