This work presents a study on the influence of the Al/Si atomic ratio in dc magnetron sputtered Al1-xSixOy amorphous and transparent films upon their chemical composition, films' structure, optical and electrical properties. Increasing silicon in Al1-xSixOy films, from 0 at% up to 31.1 at.%, caused an increment of deposition rate and an increment in Al-O-Si energy bonds as confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis. On other hand, the optical constants (refractive index (n) and extinction coefficient (k)), dielectric constant, loss tangent (tan delta) and ac conductivity (sigma(ac)) decrease when the amount of silicon in films increased. The results show that the refractive index shows small variations from linearity with vol% of Al2O3 (or SiO2). Dielectric constant and dielectric loss evidenced two dipolar contributions, attributed to defects located one at or near the substrate/oxide interface, and the other in the bulk of the oxide.