The limit cycle #utter of a two-dimensional wing with non-linear pitching sti!ness is investigated. For modelling the aerodynamic forces of the wing steady linear and non-linear models as well as an unsteady model were used. The #utter speed was calculated using the harmonic balance method and by predicting Hopf bifurcation. Analytical solutions based on the centre manifold theory and normal forms were obtained as were results given by the harmonic balance method. The analytical solutions were compared with those obtained by numerical integration. The results show that the harmonic balance method can forecast #utter speed with a good accuracy while analytical solutions based on centre manifold theorem are accurate only in a small neighbourhood of the bifurcation point. The oscillation of the airfoil after #utter for two di!erent models, linear and non-linear pitching sti!ness were compared with each other and the #utter speeds for two linear steady and an unsteady aerodynamic model calculated. The obtained results show that #utter analysis based on the linear steady model is conservative only for the ratios of plunge frequency to pitch frequency lower than 1.