This article reports on an investigation of microwave radiation copolymerization of dibutyltin maleate (DBTM) with allyl thiourea (AT) and the copolymers it produced. The effect of radiation energy, composition of monomer, amount of initiator, and amount and kind of inorganic oxide (Al2O3, or SiO2) as reaction sensitizers on the copolymerization conversion and polymer-inherent viscosity were systematically studied, and simultaneously compared with the relevant conventional thermopolymerization. The reactivity ratios for DBTM and AT were determined using liquid chromatography. The copolymerization mechanism of microwave radiation was probed using a free-radical capturing agent (DPPH). The copolymers obtained were used as heat-stabilization agent of PVC resin.