Poly(butylene succinate) (PBSu) and two poly(butylene succinate-co-propylene succinate)s 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 H-1 NMR. 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 degrees C/min. Morphology and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve-fitting. 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 degrees C 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. 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. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1299-1308, 2010