The mechanical properties of epoxy systems filled with natural zeolite were studied. To study the effect of the filler content and particle size, natural zeolites of three different particle sizes were added to epoxy resin at various contents. The effect of strain rate on the tensile strength was also tested. With increasing zeolite content, Tg and Young＇s modulus increased; however, tensile strength and impact strength decreased. As the zeolite particle size decreased, all these properties increased, and tensile strength increased, with increasing strain rate. The fracture surface of the composite showed more complex morphology with increasing zeolite content.