In this study, fabrication of poly(vinylidene fluoride) (PVDF) flat sheet membranes and correlation of membrane morphology, roughness, crystalline structure, and pore diameter distribution as functions of coagulant temperature (T-C) and precursor-solution preparation temperature (T-S) in the phase inversion (PI) process of PVDF-DMF-H2O mixture with 20% wt of PVDF concentration was investigated. The results demonstrated that membranes have a typical asymmetric structure with a dense skin top layer and a porous substructure. An increasing amount of macrovoids was observed in the membrane substructure when T-S is decreased. It was found that at lower T-C, the membrane solution precipitated into a uniform morphology composed of spherical crystallites that exhibited the beta-form crystal structure. By contrast, when PVDF was precipitated at higher temperatures, the formed membrane became largely in the alpha-form crystal structure. The pore size was estimated by Barett-Joyner-Halenda (BJH) method, ranging from 15 nm to tenth of hundred nm, depending on T-C. The performance of the prepared membranes has been tested by the measure the effects of T-C and T-S on the separation characteristic of nanoporous PVDF membranes. We observed that the removal of Acid Yellow 23 (AY23) decreases as T-S increases and extremely high dye removal efficiency of 99.37% was achieved.