Plasma sprayed micro-structured Al-Si based and 1 wt% nano-structured Si3N4 coating was successfully fabricated on an AZ31B magnesium alloy using a high efficiency supersonic atmosphere plasma spraying system, and then the as-sprayed coating was remelted by a continuous wave CO2 laser. The remelted coating was investigated by optical microscope, scanning electron microscope, energy-dispersive spectroscopy, X-ray diffractometer and Vickers microhardness tester. The results indicated that the laser remelted coating possessed an excellent metallurgical bonding to the substrate. A finer dendritic structure was exhibited after laser remelting. The nano-Si3N4 decomposed fully in the coating, and the remelted coating was mainly composed of Al, AlN, Al9Si, Al3.21Si0.47 and Mg2Si. Moreover, the microhardness of remelted coating was enhanced to 200-514HV(0.05), which was much higher than that of the substrate(about 50 HV0.05). (C) 2013 Elsevier B. V. All rights reserved.