The influence of unsaturated polyester resin to sand ratios as well as γ-irradiation on the physico-mechanical properties of the sand-polyester composite has been investigated. The samples were prepared at different ratios ranging from 5% to 30% of unsaturated polyester to sand, then subjected to γ-irradiated between 10 and 100 kGy. The effect on the compressive strength, total porosity, and water absorption, in addition to infrared spectroscopy and thermogravimetric analysis (TGA) were studied. The results indicate that the compressive strength increases with the increase of unsaturated polyester resin and the γ-irradiated dose, whereas the total porosity and water absorption values were decreased. These are attributed to adhesion between the sand and unsaturated polyester under the effect of γ-irradiation. Infrared spectra showed the appearance of new bands as a result of the formation of the Si=C bond. Also, TGA showed that the thermal stability of the composite increases with the increase of exposure dose.