Abstract: An improved method for the determination of the stability constants of complexes has been presented by combining the principles of pH-potentiometric method and the method of simultaneous measurement of pH-pMvalues. Only pHvalues have to be measured during the titration, but the volumes of the titrant added be recorded. The method has been applied to complex system Cd(Ⅱ)-Citric acid at 25±0.5℃ and the ionic strength 1.0. The results arc practically consistent with the values obtained by previous works.