The effect of EB radiation on the mechanical properties of HIPS matrix nanocomposites is discussed in this paper. Two different types of clays were used (calcic Cuban and sodic Brazilian bentonites) as reinforcement material, in 5 and 7% additions regarding the weight of the material. All clays used were subjected to organic modification. Composite material pellets were prepared in a hot extrusion process adding the clays aided by a vibrating dispenser. Mechanical test samples, for tensile and impact tests, according to ASTM standards, were elaborated in an injection molding machine. Half of the samples were irradiated at 600KGy and seven days later, they were tested. The rest of the specimens were tested from their direct injection state. It was shown that an addition of up to 5% of clay as reinforcement in a matrix of HIPS achieved increases in tensile strength over 30% compared with the unreinforced polymer. Additions of higher amounts of clay (7%) represented a decrease on mechanical strength, compared with the 5% addition. Electron beam irradiated samples showed a considerable increase in the tensile strength with respect to this strength in pure material. Increases between 48 and 56% were achieved. In all cases elongation and impact strength decreased with the aforementioned increase in tensile strength..