Double layer coatings, with celsian-Y2SiO5 as inner layer and Y2Si2O7 as outer layer, were prepared by microwave sintering on the surface of carbon fiber reinforced silicon carbide matrix composite. Both celsian, Y2SiO5 and Y2Si2O7 were synthesized by in situ method using BAS glass, Y2O3 and SiO2 as staring materials. The sintering temperature was 1500 degrees C, and little damage was induced to the composite. The composition and micrograph of the. red coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The oxidation and thermal shock resistance of samples with doubled-layered coating were characterized at 1400 degrees C in air. After 150 min oxidation and thermal cycling between 1400 degrees C and room temperature for 15 times, the weight loss of double layer-coated sample was 1.22% and there were no cracks in the coating. (C) 2008 Elsevier B.V. All rights reserved.