This paper deals with the preparation and characterization of novel organic-inorganic composite membranes formed by fine silica particles uniformly dispersed in the porous matrix of poly(vinylidene fluoride). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments, burst pressure tests and scanning electron microscope (SEM) observations. Spectroscopic (FTIR-ATR, FT-Raman) and calorimetric (DSC) measurements were also carried out in order to investigate interactions between membrane components. Supported membranes were finally prepared and their ultrafiltration performance was compared with that of unsupported ones.