A two-stage reduced-dimension space-time adaptive processing (STAP) method fo r clutter suppression in airborne multiple-input multiple-output (MIMO) radar is proposed. The Doppler filtering method is firstly performed to reduce the dat a dimension in temporal domain. Then the weight vector of the two-dimensional t r ansmit-receive beamformer is decomposed into the Kronecker product of the trans mit and the receive weight vectors. The two low-dimensional weight vectors are res olved respectively to synthesize the final weight vector. The proposed method ca n significantly decrease the training sample requirement and the computational l oad. Under the small sample number condition the method can provide a good clutt er suppression performance, so it has greater value in practical applications. S imulation results verify the effectiveness of the proposed method.