The diffusion coefficients of boron in amorphous silica (SiO2) films have been determined over the temperature range from 1173 to 1373 K. The SiO2 films were prepared by thermal oxidation of silicon substrates. Boron was incorporated into the SiO2 films from boron vapor, the pressures of which were varied between 5.5 X 10(-18) and 7.2 X 10(-13) Pa. The diffusion coefficients were calculated from boron concentration profiles in the SiO2 films measured using secondary ion mass spectrometry : D-B/m(2) s(-1) = 1.88 X 10(-12) exp (-205,000/RT), where R is 8.31 J K-1 mol(-1). The diffusion coefficients were not dependent upon boron vapor pressures, i.e., the boron concentrations at the film surface. The discussion on the activation energy and chemical state analysis using x-ray photoelectron spectroscopy offer the mechanism that boron diffuses through the silicon sites in the network of SiO2.