Buffer system, exhaustion and reduction behavior of indigo dye, and dyeing properties under real dyeing conditions were investigated to develop a dyeing technique for cotton denim garment. The pH of dye bath was maintained between 10-12 by the new buffer system composed of sodium carbonate and formic acid. The reduction rate of indigo dye by sodium hydrosulfite in the buffer system was sufficient and increased with increasing temperature and decreasing pH. The amount of absorbed leuco indigo dye increased with decreasing the dyeing temperature and pH. The pigmentation dyeing method, in which reducing agent is added portionwise to the dye bath, was found to be the most effective dyeing technique for cotton denim fabric.