High　velocity　arc　spraying　(HVAS)　process　was　used　to　deposit　Al-Ni-Y-Co　and　Al-Ni-Mm-Fe　amorphous/nanocrystalline　composite　coatings　onto　AZ91　Mg　alloy　substrate.　Their　microstructure　was　characterized　by　using　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM)　and　transmission　electron　microscopy　(TEM).　The　coatings　are　both　about　500　mu　m　in　thickness　with　fully　dense　and　low　porosity.　The　microstructure　of　the　coatings　is　classified　into　two　regions,　namely,　a　full　amorphous　phase　region　and　homogeneous　dispersion　of　fcc-Al　and　some　intermetallic　nanoscale　particles　in　a　residual　amorphous　matrix　region.　Vickers　micro　hardness　of　the　coatings　was　also　measured.　The　average　Vickers　micro　hardness　of　Al-Ni-Y-Co　and　Al-Ni-Mm-Fe　coating　is　about　311　HV　and　340　HV,　respectively.