A ruthenium‐catalyzed ammoxidation of alkenyl oximes under mild and neutural condtions is described. In this method, tert‐butyl nitrite plays a dual role, acting as an oxidant as well as a nitrogen source. This reaction avoids using any toxic radical initiators or cyanide reagents. This convenient and practical method offers an easy access to 5‐cyanated isoxazolines in good to high yields, and shows good functional group tolerance and high efficiency. It is rather remarkable that this new reaction provides a strategically distinct approach based on non‐stabilized radical intermediate and constructs C–O and C≡N triple bonds in a single‐step. Moreover, the difunctionalization of unactivated olefins bearing oximes has been realized.