A chemical method and an improved absorbance ratio method are presented to determine the degree of neutralization of poly(ethylene-co-methacrylic acid). Compared to the chemical method, the absorbance ratio method is simple and fast. It can be used also to determine the degree of neutralization when the chemical method is not suited to the system. By means of this absorbance ratio method, the influences of various reaction conditions on the rates of neutralization were observed. In the neutral system at the optimal water content a maximal rate of neutralization is obtained. The rate of neutralization is increased by increasing the temperature or the concentration of metal hydroxide or by decreasing the concentration of the copolymer.