Poly(vinylidene fluoride)(PVDF)/nano-sized TiO2/carboxy-methylcellulose (CMC) organic-inorganic composite ultrafiltration membranes were prepared by phase-separating method.The influence of the additive amounts of nano-sized TiO2 and CMC on the properties of organic-inorganic composite membranes were investigated through the methods of SEM, porosity analysis and ultrafiltration experiments. The results showed that the PVDF/TiO2 /CMC composite membranes exhibited differences in morphologies and properties due to nano-sized TiO2 and CMC addition. At 2wt.% TiO2 and 4wt.% CMC, the composite membranes were of uniform microstructure and held excellent water permeability, while the addition of TiO2 over 3 % and CMC to 6 %, nanoparticles of the composite membranes appeared agglomeration, the porosity and ultrafiltration properties would decline.