Abstract: Polymethyl phenyl vinyl siloxane rubber(MPVQ) has excellent performances of resistance of high or low temperatures and vibration abatement, etc., it should have spread application to spacecraft vibration abatement and seal. The total ionizing dose effects of MPVQ have been investigated. The results show that the mechanical properties have different degradation with the increase of the irradiation dose. The dose of 1106 Gy(Si) is the change point for the tensile strength and the tear strength. Lower than this dose, the tensile strength and the tear strength decrease quickly with the increasing dose. Higher than this dose, the tensile strength rebound slightly, presenting a wide U distribution; and the tear strength firstly increase and then decrease with the accumulated dose. The elongation at break and Shore A hardness quickly decrease and increase with the total dose respectively, and finally they are close to saturation. The underlying mechanism of total ionizing dose effects for MPVQ is discussed in terms of radiation crosslinking and radiation degradation.