In this study, linear low-density polyethylene (LLDPE) and polypropylene (PP) were dry-blended with ground tire rubber (GTR) respectively to produce two types of composites by rotational molding. Different GTR concentrations (0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50% wt.) were incorporated into these rotomolded composites, which were then characterized with respect to morphology, density and mechanical properties (tensile, flexural and impact). As expected, due to the incompatibility between GTR and thermoplastic matrix, an increasing number and size of bubbles with more defects were generated in these two types of composites with increasing GTR content. Besides, with GTR content increasing, the tensile strength and modulus as well as flexural modulus of these rotomolded composites decreased. However, it is interesting that the LLDPE/GTR composites had up to 35% higher impact strength compared with neat LLDPE. Probably because of the lower chain mobility of PP molecules, which limited physical entanglement, the impact strength of PP/GTR composites decreased with increasing GTR concentration.