The melting behavior and the isothermal crystallization kinetics of poly(buty1ene adipate), poly(buty1ene isophthalate) and their random copolymers were investigated by means of differential scanning calorimetry. Multiple endotherms, commonly observed on the melting polyesters, were found to be iinfluenced by crystallization temperature and composition. By applying the Hoffman-Weeks method to the isothermally crystallized samples, the equilibrium melting temperatures of the homopolymers were obtained. From calorimetric results on samples with different degree of crystallinity, the equilibrium melting enthalpy of poly(buty1ene isophthalate) was calculated and the presence of a crystal-amorphous interphase in copolymers was evidenced. Isothermal melt crystallization kinetics was analyzed according to the Avrami equation. As expected, the introduction of a comonomer was found to decrease the overall crystallization rate of the polymers. Values of Avrami exponent close to three were obtained for all the samples, independently of composition and crystallization temperature, in agreement with a crystallization process originating from predetermined nuclei and characterized by three-dimensional spherulitic growth. In the case of poly(buty1ene 1 sophthalate), the dependence of the rate of crystallization on T, shows a maximum at an undercooling of approximately 60 "C.