Among various solid electrolytes, the lithium–phosphorus oxynitride (Lipon) electrolyte synthesized by sputtering of Li3PO4 in pure N2 has a good ionic conductivity of 2(±1)×10−6 Scm−1 at 25°C. As the nitrogen concentration increases in the Lipon electrolyte, the ionic conductivity is reported to increase as a result of a higher degree of cross-links. When Lipon films are deposited by sputtering, however, it is reported that the maximum nitrogen concentration saturates approximately at 6at.%. By non-equilibrium processes, such as ion-implantation, nitrogen concentration can be controlled over 6at.%. This study investigates the effect of nitrogen concentration on the ionic conductivity in Lipon films by using ion-implantation. Impedance measurements at 25°C show that the nitrogen-implanted Lipon films enhance or retard the ionic conductivity over a wide range after nitrogen-implantation, when compared with as-deposited thin-films.