We obtain some microlocal estimates of the resonant states associated to a resonance z 0 of an h-differential operator. More precisely, we show that the normalized resonant states are O( |Im z 0 |/h +h ∞ ) outside the set of trapped trajectories and are O(h ∞ ) in the incoming area of the phase space.As an application, we show that the residue of the scattering amplitude of a Schrödinger operator is small in some directions under an estimate of the norm of the spectral projector. Finally we prove such bound in some examples.