Six kinds of poly(silyleneethynylenephenyleneethynylene)s [-Si(R)H-C=C-C6H4-C=C], wherein the phenylene group was the meta-, para- or ortho-form and R represents a phenyl, methyl, or hydrogen atom, were prepared, and the properties of the resulting polymers were investigated. The polymers, especially poly[(phenylsilylene)ethynylene-1,3-phenyleneethynylene] (R=Ph), which were thermosetting, soluble in solvent, fusible, and moldable, showed high heat-resistant and burning-resistant properties. A cross-linking reaction mechanism concerning the Si-H and C=C bonds was proposed, and the correlation between the molecular structures and the thermal properties was discussed. Fiber-reinforced polymers prepared using glass, carbon, or SiC fibers showed sufficient mechanical strength even at 400 degrees C under air. A black, hard, and glassy material (C-SiC) was obtained when poly[(phenylsilylene)ethynylene-1,3-phenyleneethynlene] was heated above 1000 degrees C under argon.