The influence of gamma radiation on the morphology, thermal, mechanical and rheological properties of blends of high density polyethylene/low density polyethylene (HDPE/LDPE) was investigated. Prior to irradiation blends of different thermal history were prepared by fast cooling and slow cooling from the melt. Results showed that there were not significant changes in the degree of crystallinity of the blends with radiation. Higher values of degree of crystallinity and melting peak temperature were obtained for the slowly cooled blends. A small increase in the Young modulus and the yield stress were observed by irradiating the blends, and the elongation at break was reduced about 70% when compared to non-irradiated blends. High degree of crosslinking is expected to occur due to the decrease in melt flow rate of the blends irradiated to 50 kGy, and no flow was detected at 150 kGy. Transmission electron microscopy observations failed to show important changes in morphology with radiation.