Fiber cement board has been increasingly used in the building construction in order to reduce the construction time and to control the building quality according to the required standard. However, the color cracking of painted fiber cement board is usually found in the production, and it is totally unacceptable. Hence, this research aims at decreasing the defective products due to the color cracking in the painting of fiber cement board. According to the study, the humidity of fiber cement, bending of fiber cement panel and thickness of top coat were the main factors affecting the color cracking on the painted fiber cement panel. By optimizing the painting process under the manufacturing constraints, the color cracking can be minimized when the humidity of fiber cements was 11.5 %RH, the warp of fiber cement was 0 mm and the thickness of top coat was 3 mm. With the use of this optimum condition, the proportion of defective products due to color cracking can be reduced from 4.84% to 1.17%.