AbstractPoly-(vinylidene fluoride) (PVDF), which has a low surface energy, is a common material used for ultrafiltration (UF) membranes. Bacterial cellulose (BC) contains a large number of hydroxyl groups, which has a strong water holding capacity. It can improve the hydrophilicity of PVDF. By means of in-situ composite preparation, with the introduction of tetraethoxysilane (TEOS) as silicon source from the outside of BC and polymerizing, hybrid reinforcing material comprised of BC and silica (BC/SiO2) was achieved which were catalyzed by different acids. After that, by means of a phase separation method with PVDF, composite membranes (PVDF/BC/SiO2) were prepared. Visible spectrophotometry, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were used to investigate the characteristic of BC/SiO2 hybrids. The structure and properties of composite membranes were also investigated. After catalysis by acid, SiO2 particles uniformly adhered to the surface of BC fibers, which resulted in small pores being formed preferentially in the interface of PVDF composite membranes, while reducing the finger-like pores. At the same time the retention of the composite membranes were improved. So both the properties and structure were improved due to the presence of certain BC/SiO2 hybrid reinforcements.