Styrene-maleic anhydride copolymer is a synthetic copolymer with interesting features from both the chemical and the biological points of view. The proportion of maleic anhydride is an important factor that influences its function. The structure of styrene-maleic anhydride copolymer was determined to be monocarboxyl/monocarboxylic salt by potentiometric and conductometric titration. The titration end point was determined by derivative method. A simple and speed potentiometric titration method was established according to that. This method was proved precise by element analysis.