Abstract: The present paper reports the studies of the alkaline polycondensation kinetics of poly (phenylene ether sulfone). The related monomers and their model compounds for polymers were synthesized, then their reaction velocity constants were determined. The chief results obtained are. (1) when two series (m,n) of substituted benzene derivatives are reacted with each other, the velocity constant k_mn is equal to the product of velocity constant k_m0 and k_n0.(2) For polycondensation reaction, when the reactivities of the monomers and the polymers are different, as in the case of polycondensation of poly (phenylene ether sulfone),it is not quite accurate to use a single velocity constant to derive the kinetic equation, instead, two or more reaction velocity constants must be used so as to conform to the experimental facts.