This thesis work has the aim to study a rotor disk of a compressor for aeronautical applications. It's known, that if a rotor disk of a compressor is considered, from a failure point of view, the blades are the most critical component. The main cause derives mostly from vibrations generated from external forces. This phenomenon it's cause of a reduction of the time to failure of the compressors. In this thesis, first some theory about systems of compressor and mistuning is given. This helps to understand the dynamic behaviour of a rotor disk and how it changes when the geometry of the disk is slightly different from the nominal one and cannot be modelled under cyclic symmetry conditions.