Abstract: Some oxygen containing groups such as C —O , C=O and —OH were int roduced onto the molecularchains of linear low-density polyethylene (LLDPE) through ult raviolet irradiation in air without other additives andchemical pollution. These groups content s increase with the ult raviolet irradiation time. Af ter the ult raviolet irradiation , the crystal shape and distance of the crystal plane of LLDPE remain unchanged. However , the melting temperature and crystallinity decrease. Compared with those of LLDPE/ nylon66 (PA66) composites , the dispersion ofirradiated LLDPE in irradiated LLDPE/ PA66 composites and the compatibility between irradiated LLDPE and PA66and interfacial interaction are improved obviously. The mechanical properties of irradiated LLDPE/ PA66 compositesinitially increase and then decrease with increasing the irradiation time. Their maximums are obtained when the irradiation time was 24 h. The tensile st rength , bending st rength and notched impact st rength of irradiated LLDPE for24 h/ PA66 composites increase by about 20 % , 13 % and 330 % compared with those of LLDPE/ PA66 composites ;the irradiated LLDPE shows higher toughening effect .