Nitrogen-incorporated lithium silicophosphate (LiSiPON) thin-film electrolytes, which contain two glass-forming elements, are fabricated by sputtering from a (1−x)Li3PO4·xLi2SiO3 target in a nitrogen reactive plasma. The results of impedance measurements show that the activation energy for conduction decreases as the Si content increases, which leads to an increase in the ionic conductivity of the films. It is suggested that these improvements in the electrical properties of the films are due to the combined effect of the mixed former and nitrogen incorporation. It appears that the decomposition potential of the electrolyte film in contact with Pt is about 5.5V.