The influence of chemical structure of Benzopurpurine 4B and Congo Red on the color fastness properties of cotton fabric have been studied at $90^{circ}C$. Each dyeing carried with $10 imes10^{-6}M$ of dye concentration and 0.1 M of NaCl. The results obtained from this study were as follow; 1. The properties of fastness to washing by Benzopurpurine 4B were superior to those of Congo Red. 2. The properties of fastness to light by Congo Red were superior to those of Benzopurpurine 4B. 3. The color variation appeared more vividly in the case of Benzopurpurine 4B than Congo Red and the color shifted to Red Purple after washing test but to Yellow Red after Fade-O-meter test.