A vinylidene fluoride resin having a weight-average molecular weight as
relatively high as 300,000 or higher is mixed with a plasticizer and good
solvent for the vinylidene fluoride resin to obtain a composition. A
molten extrudate of the composition in a hollow-fiber membrane state is
contacted, on its outer side, with a cooling liquid inert to the
vinylidene fluoride resin to thereby cool the extrudate. During the
solidification, the vinylidene fluoride resin is moderately and mildly
crystallized. Thus, a hollow-fiber porous vinylidene fluoride resin
membrane is produced which has a high crystallinity represented by an
enthalpy of crystal melting 58 J/g or higher. The hollow-fiber porous
membrane obtained is excellent in mechanical strength represented by
tensile strength and elongation at break and in chemical resistance. It
is effectively used as a water microfiltration membrane.