The effects of aluminum-ion-implantation on the oxidation behavior of NBD 200 Si3N4 were investigated over an implant concentration range of 0-30 at.%, at 800degrees-1100degreesC, in 1 atm dry O-2. Oxidation of both unimplanted and implanted samples follows a parabolic rate law. The parabolic rate constant decreases and the activation energy increases with aluminum concentration. Smooth and crack-free oxides are formed under the combination of high implant concentrations and low oxidation temperatures. Outward diffusion of Mg2+ from the bulk of NBD 200 to the oxide layer remains the rate-limiting step for aluminum-implanted samples. The enhancement of the oxidation resistance of NBD 200 by aluminum implantation is attributed to the retardation of the outward diffusion of Mg2+.