In the dyeing of cotton and silk fibres using Caesalpinia sappan, the effects of pH changes of the Caesalpinia sappan dye liquor on the color were examined. In order to adjust the pH of the Caesalpinia sappan dye liquor, Schisandra chinensis extract and carboxylic acid were used for acidic condition, lye and the NaOH aqueous solution were used for alkaline condition. By introducing the dyeing method of pH adjustment, firstly, the effect on the reddish color inherent to the Caesalpinia sappan was examined. At the same time, the manifestation of the yellow color, which affect the manifestation of the red color greatly, was examined in detail quantitatively. By dyeing the cotton and silk fabrics, the inherent relationships established between the pH hanges and the fibre characteristics were sought to be examined.