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Fly ash microspheres and carbon black were taken as raw materials to prepare SiC/Mullite microspheres by microwave heating carbon thermal reduction. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were applied to characterize the phase composition and microstructure of SiC/Mullite spheres.The phase composition and the structure were characterized by XRD and FESEM. The results show that the reaction mechanism mainly associates with solid-solid reaction between C(s) and SiO2(s) on the surface of fly ash microspheres with its spherical shape unchanging when the temperature is between 1100-1300 oC. When the temperature is higher than 1300 oC, SiC has easier orientation growth into whisker through VLS mechanism for the presence of liquid phase. Mullite is involved in the reaction; therefore, fly ash microspheres cannot maintain its spherical shape. The optimum conditions of our experiments are n(C):n(SiO2)=4.2, 1200 oC and 1 h