A kinetic study of poly(butylene terephthalate) polymerization from dimethyl terephthalate and butanediol, using a catalyst mixture composed of titanium tetrabutoxide and hafnium acetylacetonate, in 1:3 molar ratio, was performed and compared to the standard titanium only catalyst. Arrhenius parameters were obtained from model reactions for both stages of polymerization. The mixed catalyst showed a consistently higher pre-exponential factor (A) and a higher activation energy (E-a) in the Arrhenius equation compared to the industrially used catalyst. For this reason the mixed catalyst, as observed in actual polymerizations, is more active at high temperature.