Crystal structure and morphology development of poly(butylene oxalate) (PBOX) during isothermal crystallization were studied with X-ray diffraction, time-resolved simultaneous small-angle X-ray scattering, differential scanning calorimetry, and optical microscopy. Results indicate that the decrease in the long period at low crystallization temperature indicated the occurrence of secondary crystallization in the interlamellar space. Meanwhile, the lamellar thickness slightly increased with crystallization temperatures due to the formation of thicker crystalline layers at high temperatures. The crystal growth rate of PBOX was analyzed by optical microscopy. Using values of the equilibrium melting temperature of 117.4 degrees C and the fold surface free energy of 32.37 erg/cm(2) obtained by the Gibbs Thomson theory, the nucleation parameter, K-g, of 97264 K-2 and the lateral surface free energy of 17.68 erg/cm(2) were determined from the Lauritzen and Hoffman equation. These values are comparable to various semicrystalline polymers previous reported and are not available up to now for PBOX in the literature. (C) 2013 Elsevier Ltd. All rights reserved.