Fiber reinforced plastics (FRPs), reinforced with carbon fiber, SiC fiber and glass fiber, were prepared by using a new thermosetting silicon-containing polymer, poly[(phenylsilylene) ethynylene-1,3-phenyleneethynylene](MSP), as a matrix resin. In MSP composite processing, no solvent is needed, no by-products are generated, and the curing temperature is low (150-210degreesC). The FRPs (MSP composite) showed high heat-, burn-and radiation-resistant properties. Bending strengths (110-140 MPa) and modulus (30 GPa) at 200degreesC and 400degreesC were almost equal with those at room temperature, and were not affected by 100 MGy of irradiation. Dynamic viscoelasticity and creep properties of MSP composite were also determined and compared with those of a polyimide composite.