A polyester resin composition having improved neutron shielding properties can be made by mixing a condensation product of maleic anhydride, phthalic anhydride and polyethylene glycol dissolved in styrene, with at least a sufficient amount of pelleted polyethylene to substantially increase the neutron shielding properties of said condensation product, and a sufficient amount of curing agent such as benzoyl peroxide and N,N-dimethylaniline to promote the curing of the mixture to a solid product. The polyethylene having a relatively high hydrogen content reduces the energy of the neutrons. A powdered boron compound such as boric acid and/or a lithium compound can be incorporated in the composition in amounts at least sufficient to effect substantial thermal neutron capture. Cadmium can be incorporated into the composition being much more efficient at neutron capture than boron or lithium, but then provision must be made for stopping the capture gamma rays generated.