Poly(vinylidene fluoride) (PVDF) membranes were prepared by the immersion precipitation method. Effects of the maturation time of dopes on the morphology and crystallization of the prepared membranes were investigated. The analysis showed that the maturation time played an important role in determining the morphology of the prepared membranes. For the dope prepared in the initial day, liquid–liquid demixing preceded solid–liquid demixing in the process of the membrane formation. The morphology of the cross section of the prepared membrane (M1) was finger-like structures with a sponge substrate beneath the porous skin. During the maturation, the dopes underwent a microscopic phase separation and the PVDF crystallized, which resulted in the existence of micro-liquid phases and micro-solid phase crystalline areas in the dopes. In the process of the membrane formation, liquid–liquid demixing took place by nucleation and growth of droplets of the polymer rich phase in the micro-liquid phase. The micro-solid phase crystallites were connected together by the polymer chains, and formed a three-dimensional network gelation morphology. The crystal structure of M1 was mainly β crystals. With increasing maturation time of the dopes, the proportion of β decreased crystals, but that of α crystals increased for the prepared membranes.