Poly(butylene succinate) (PBSu) and two poly(butylene succinate-co-propylene succinate)s (PBPSu 95/5 and PBPSu 90/10) were synthesized via the direct polycondensation reaction. The copolyesters were characterized as having 7.0 and 11.5 mol% propylene succinate (PS) units, respectively, by 1H NMR. Copolyesters were characterized as random, based on 13C NMR spectra. They were fully investigated during nonisothermal crystallization and thermal degradation through various approaches in this study. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) adopted to study the nonisothermal crystallization of these polyesters at a cooling rate of 1, 2, 3, 5, 6 and 10 ºC/min. Morphologies and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve-fitting, respectively. These continuous rate data were analyzed with the Lauritzen-Hoffman equation. A transition of regime II ¡÷ III was found at 95.6, 84.4, and 77.3 ºC for PBSu, PBPSu 95/5, and PBPSu 90/10, respectively. DSC exothermic curves show that all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman and Vyazovkin equations. Ozawa equation does not accurately describe the nonisothermal crystallization kinetics of this polyester because part of the crystallization is secondary crystallization. All the results of PLM and DSC measurements indicate that incorporation of minor PS units into PBSu markedly inhibits the crystallization of the resulting polymer. The melting behavior of nonisothermally crystallized samples presents a continuous melting¡Vrecrystallization¡Vremelting process. Additionally, three absorption bands during the nonisothermal crystallization were identified for PBSu and two PBPSu copolyesters, namely, 916, 955, 1045 cm-1 in the attenuated total reflectance FTIR spectra. Thermogravimetric analysis (TGA)-FTIR was heated at 5 ºC/min under N2 to monitor the degradation products of these three polyesters. FTIR spectra revealed that the major products were anhydrides, which were obtained following two cyclic intramolecular degradation mechanisms by breaking the weak O-CH2 bonds around a succinate group. Thermal stability at heating rates of 1, 3, 5, and 10 ºC/min under N2 was investigated using TGA. The model-free methods of Friedman and Ozawa equations are useful for studying the activation energy of degradation in each period of mass loss. The results reveal that the random incorporation of minor PS units into PBSu did not markedly affect their thermal resistance. Two model-fitting mechanisms were used to determine the loss mass function f(£\), the activation energy and the associated mechanism. The mechanism of autocatalysis nth-order, with f(£\)=£\m(1-£\)n, fitted the experimental data much more closely than did the nth-order mechanism given by f(£\)=(1-£\)n. The obtained activation energy was used to estimate the failure temperature (Tf). The values of Tf for a mass loss of 5% and an endurance time of 60,000 hr are 160.7, 155.5, and 159.3 ºC for PBSu and two the copolyesters, respectively.