AbstractLiquid polycarbosilane substituted by allyl groups was prepared by the Grignard coupling reaction and reductive reaction synthesis with SiCl1.25(OCH3)1.75CH2Cl, Cl2CHSiMeCl2 and CH2=CHCH2Cl as the starting materials. The resultant polycarbosilanes were characterized by gel permeation chromatography, Fourier transform infrared and NMR spectroscopy. Moreover, the thermal properties and processing performance of polycarbosilanes were investigated. The ceramic yield of polycarbosilanes was about 77% at 1000°C, indicating that the polycarbosilanes have great potential to be promising precursors to SiC. With the increase of Cl2CHSiMeCl2 in the system, the viscosity of polycarbosilanes and C : Si ratio of ceramics increased, but the ceramic yield of polycarbosilanes decreased. Combining with its economical preparation, polycarbosilanes showed high potential as an economical SiC ceramic precursor for the fabrication of SiC matrix, coating and adhesives.