Polylactide (PLA)/silica composite films were prepared by two methods: blending nanoscale colloidal silica sol and sol-gel. The nano and microscale silica particles, respectively, were well dispersed in PLA when observed using scanning electron microscopy and transmission electron microscope. The mechanical and thermal stability of composite films were measured before and after hydrolysis by Instron and thermogravimetric analysis. The fillers increase tensile strength, Young's modulus, thermal stability, and hydrolysis resistance with increasing silica content. The nanoscale particles exhibit better effects than the rnicroscale ones. The activation energy, E-a, of thermal decomposition is also simulated by the Kissinger and Ozawa equation. The results also show that the thermal stability is increased by the incorporation of silica particles and is lowered by hydrolysis. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1688-1694, 2009