Diagnosability have played an important role in measuring the reliability of multiprocessor systems. As an enhancement on the hypercube, the augmented cube, not only retains all the favorable properties of the hypercube but also possesses some properties which are not shared by the hypercube and its variations. In this paper, under the PMC model, we prove that the n-dimensional augmented cube AQn is (2n-1)-diagnosable under the precise diagnosis strategy and (4n-8)/(4n-8)-diagnosable under the pessimistic strategy (n>6).