Poly(vinylideneflouride) (PVDF)/nano-titanium dioxide (TiO₂) composite membranes were prepared via a phase inversion method by dosing different amounts of TiO₂ nanoparticles in PVDF casting solution to improve the antifouling ability. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and the quartz crystal microbalance with dissipation (QCM-D) monitoring were adopted to clarify the antifouling behaviours of the composite membranes. The results showed that the addition of nano-TiO₂ could improve the membrane surface porosity, volume porosity, hydrophilicity and permeability. The electron donor monopolarity of the composite membranes was evidently enhanced, and the repulsive interaction energy barrier between foulants and membrane surfaces was increased by adding TiO₂ nanoparticles, thus improving the antifouling ability. The optimal dosage of TiO₂ nanoparticles was 0.05 wt% for the composite membranes. It was also found that when the TiO₂ concentration was higher than 0.05 wt%, the aggregated TiO₂ nanoparticles dispersed inside the membrane increased the roughness of the pore wall and lowered the energy barrier between foulants and the membrane inner surface, which allowed more foulants to adsorb into the membrane pores.