Mixed-bed ion exchange performance was studied experimentally with variations of cation to anion resin ratio, resin weight and temperature at ultralow sodium chloride solution concentrations of less than 1.0×10^-4M. Analyzing the effluent concentration histories the performance test was examined as a function of tested solution volume for a laboratory-scale continuous flow column until both the cation and anion-exchange resins were exhausted. Initial leakage was observed for both cation and anion breakthrough curves, but serious at cation breakthrough curve because of low selectivity coefficient. The slope of breakthrough curve was affected by selectivity coefficient and temperature. The slope of anion breakthrough curve was steep because of the large selectivity coefficient, and ion exchange rates increased a s temperature increased. The temperature effect decreased as the total volume was increased or as the resins were exhausted.