A series of bimodal polyethylenes with different molecular weight distribution characteristics were prepared by melt blending, and the fracture behavior of these bimodal polyethylenes was studied by the method of essential work of fracture. The results show that specific essential work of fracture, We, increases obviously with the molecular weight distribution characteristic, A(L/U), indicating the improvement of the resistance to crack propagation. By means of successive self-nucleation and annealing analysis, obvious variations in the crystal structures of bimodal polyethylenes with increasing A(L/U) have been found. That is, the crystal size and the amount of relatively thick lamellas increase with A(L/U), but no large variation of crystallinities has been observed. So, the influence of A(L/U) is mainly on the crystal perfection, the improvement of which produces an enhancement of fracture toughness since more energy would be dissipated in the superior network structure constructed from crystalline zones and amorphous zones. (C) 2010 Elsevier Ltd. All rights reserved.