Poly(vinyl alcohol) (PVA)/SiO2 hybrid films were prepared through hydrolysis of tetraethoxysilane (TEOS) in the presence of PVA solution, followed by the in-situ crosslinking with formaldehyde (HCHO) in acidic circumstance. The swelling and thermal gravimetric (TG) analysis was employed to evaluate the influence of SiO2 and crosslinking on the properties of the hybrid films. The results indicate that SiO2 affects effectively the swelling property and thermal stability of the hybrid films because of both the filling and crosslinking effects of SiO2. With increasing the crosslinking time, the swelling ratio at equilibrium of the hybrid films decreases. The swelling ratio at equilibrium of the hybrid films is sensitive to the SiO2 content, which is similar to the swelling ratio at equilibrium (65~75%) for PVA and PVA/SiO2 hybrid films with enough crosslinking time (12h). Compared to the film without in-situ crosslinking, the crosslinked PVA/SiO2 film showed a lower swelling ratio at equilibrium and an increased diffusion coefficient at the initial stage of swelling.