The aim of this paper is to study the effects of mistuning o fan flutter and to compare the prediction of two numerica models of different fidelity. The high fidelity model use here is a three-dimensional, whole assembly, time-Accurate viscous, finite-volume compressible flow solver. The Cod used for this purpose is AU3D, written in Imperial Colleg and validated for flutter computations over many years. T the best knowledge of authors, this is the first time suc computations have been attempted. This is due to the fac that, such non-linear aeroelastic computations wit mistuning require large amount of CPU time and cannot b performed routinely and consequently, faster (low fidelity models are required for this task. Therefore, the secon model used here is the aeroelastic fundamental mistunin model (FMM) and it based on an eigenvalue analysis of th linearized modal aeroelastic system with the aerodynami matrix calculated from the aerodynamic influenc coefficients. The influence coefficients required for thi algorithm are obtained from the time domain non-linea Code by shaking one blade in the datum (tuned) frequenc and mode. Once the influence coefficients have bee obtained, the computations of aero damping require minima amount of CPU time and many different mistuning pattern can be studied. The objectives of this work are to 1. Compare the results between the two model and establish the capabilities/limitations of aeroelasti FMM 2. Check if the introduction of mistuning woul bring the experimental and computed flutter boundarie closer 3. Establish a relationship between mistuning an damping A rig wide-chord fan blade, typical of modern civil designs was used as the benchmark geometry for this study. All th flutter analyses carried out in this paper are with frequenc mistuning, but the possible consequences of mistuned mod shapes are briefly discussed at the end of this paper. Onl the first family of modes (1F, first flap) is considered in thi work. For the frequency mistuning analysis, the 1 frequency is varied around the annulus but the 1F mod shapes remain the same for all the blades. For the mod shape mistuning computations, an FE analysis of the whol assembly different mass blades is performed The results of this work clearly show the importance o mistuning on flutter. It also demonstrates that when using ri test data for aeroelastic validation of CFD codes, the amoun mistuning present must be known Finally, it should be noted that the aim of this paper is th study of mistuning and not steady/unsteady validation of CFD code and therefore minimal aerodynamic data ar presented.