In this study, a preliminary work was carried out to investigate the effect of annealing conditions on the crystallization behavior and mechanical properties of nonsolvent induced phase separation (NIPS) poly(vinylidene fluoride) (PVDF) hollow fiber membranes. The crystalline structures of surface layers and overall membranes were determined by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray diffraction, respectively. Differential scanning calorimetry and field emission scanning electron microscopy were employed to analyze the thermal behaviors and morphologies of membranes. It was found that the type of crystalline phase and degree of crystallinity of annealed membranes depended on the crystallization rate of PVDF, which in turn was determined by annealing temperature and cooling rate. For all the investigated membranes, the and phases coexisted in the outer surface, while PVDF mainly crystallized into phase in the overall membrane. The percentage of phase and degree of crystallinity increased with crystallization rate increase. The annealing process induced compaction of relatively thinner membranes; however, the pore structures did not collapse. The breaking strength of annealed membranes, associated with the variation of PVDF polymorphs and total crystallinity, was improved from 167 cN to 215 cN. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013