The kinetics of polymerization of propylene oxide(PO) catalyzed by zinc hexacyanocobaltate complex catalyst was studied by means of pressure measurements. All the reactions were carried out in 0.1 L autoclaves equipped with manometers．As soon as the pressure of the system began to decrease

the polymerization was considered to have been initiated．By evaluation of vapor-liquid equilibrium of toluene solutions of propylene oxide

the pressure was found to linearly depend on the PO volume fraction．Therefore

the rate of the reaction was known to be proportional to the rate of pressure decreasing. The influence of reaction temperature

catalyst and monomer concentrations on the reaction rate was investigated．It was found that the polymerization was a first order reaction to the concentration of catalyst C

but a second order reaction to that of monomer M as shown in the following equation．The rates also depended on reaction temperature while the apparent activation energy was 59.1 kJ／mol according to the Arrhenius equation．It was proposed that the epoxide monomer must be involved in the initiation stage of the polymerization．Based on this assumption a kinetic equation in which K was a rate constant was deduced in well accordance with the experimental results：Rp=KM2C.