The effects of electrolyte on dyeing properties of cotton fiber with Congo Red have been studied at 90, 70 and $40^{circ}C$. Each dyeing carried into an infinite bath with $1 imes10^{-4}$ mol/l of Congo Red and with various concentration of electrolytes. The results obtained from this study were as follow; 1. The equilibrium adsorption of dye $(C_infty)$ values decreased with increasing dyeing temperature, $C_infty$ values increased in the order KCl>NaCl>LiCl. 2. The values of apparent diffusion coefficients $(D_a)$ increased with increasing dyeing temperature, but $D_a$ values decreased in the order KCl<NaCl<LiCl. 3, $D_a$ values decreased with increasing electrolyte concentration. 4. Effect of electrolytes decreased with increasing dyeing temperature. 5. The values of standard affinities of dyeing $(- rianglemu^{circ})$, the standard heats of dyeing $(- riangleH^{circ})$, and the standard entropies $(- riangleS^{circ})$, increased in the order KCl>NaCl>LiCl. 6. Equilibrium adsorption isotherm curve were Freundlich type, and in the Equation y=a.x$^{n}$ , the values of a and n increased in the order KCl>NaCl>LiCl. 7. The value of $- rianglemu^{circ}$, $- riangleH^{circ}$, and $- riangleS^{circ}$, decreased with increasing electrolyte concentration.