Quasibinary asymmetric polymer blends (the average chain lengths of one component being 100 while the other is varied between N=1 and N=100) well below the critical temperature were simulated on a five-way cubic lattice using the Monte Carlo method. The bulk density was kept constant by adjusting the energy parameter epsilon according to a power law epsilon similar to N-0.8. Quantities employed for the characterization of the interface region were its thickness (calculated from the shape of the density profile), the cavity structure (evaluated from the number of heterocontacts) and the roughness of the interface (described by the relative surface enlargement and some sort of fractal dimension). In general, the interface region becomes thinner, the roughness decreases, and the cavity structure becomes less pronounced with decreasing average chain length of one component, due to the reduced degree of entanglement in the interface.