In this study, gradient cellular centresymmetric auxetic configurations are evaluated as potential cores for aeroengine fan blades, and optimized to reduce the dynamic response for the first three fundamental modes. Auxetic (negative Poisson’s ratio) re-entrant cellular beams are modeled, manufactured, and tested to assess their natural frequencies and mode shapes. Gradient versions of these beams with a varying internal cell angle are then designed to be incorporated as fillers in a baseline fan blade model. The optimized configurations of the gradient core lead to a substantial decrease of the mass of the fan blade, reduction of the dynamic modal displacements, and a lowering of the first three natural frequencies within the admissible frequency bandwidth.