Polypropylene and Nylon 66 as well as their short glass fiber-reinforced counterparts were irradiated by a mixed radiation field up to 3.0 MGy in the pool of a SLOWPOKE-2 research nuclear reactor. The mixed radiation field consisted mainly of high energy electrons and gamma rays in addition of a small part of recoiled protons, thermal and fast neutrons. Through various characterization methods such as density and melting temperature measurements, tensile testing, it was found that all studied materials underwent predominant effects of crosslinking over chain scission within their amorphous regions. Even though the radiation process was performed under a normal atmosphere with the presence of absorbed water, it appeared that the properties of irradiated materials were not appreciably deteriorated up to the maximum dose investigated.