Amorphous films in the system SiO2–AlPO4were prepared by means of the rf‐sputtering method, and their physical properties, such as density, refractive index, and temperature coefficient of Young's modulus, and infrared spectra were measured. Also, theKα X‐ray emission spectra of silicon and aluminum were measured in order to investigate the coordination state of these cations in the amorphous films. The density and the refractive index were close to those of amorphous SiO2and AlPO4and the compositional dependence showed a small deviation from linearity. The temperature coefficients of Young's modulus were positive for all of the samples. The infrared absorption spectra of all of the samples were similar to those of SiO2glass and amorphous AlPO4film, and there was no evidence of the presence of P═O bonds. The coordination states of silicon and aluminum ions in the present amorphous films were the same as those in fused silica and AlPO4crystal, respectively. The results of the properties, infrared absorption spectra, and X‐ray emission spectra suggest that SiO4tetrahedrons and AlO4–PO4connecting tetrahedral dimers constitute the network of the present amorphous films. A small deviation of the physical properties from an additive rule was thought to result from the difference in the bond character between the newly formed Si–O–Al and Si–O–P bonds and the bonds in the end members