A ductile-to-semiductile transition in the crack resistance behaviour of PP/MWNT composites is discussed, using an essential work of fracture a proach based on a post yield fracture mechanics concept and its possible interrelation to the structural attributes studied by TEM, SEM, and WAXD. A maximum in the non-essential work of fracture is observed at 0.5 wt.-% MWNT content, which demonstrates the enhanced resistance to crack propagation compared to pure PP, followed bv a sharp decline with the increase in MWNT content to 1.5 wt.-%, which reveals a ductile-to-semiductile transition. Fracture kinetic studies present a qualitative picture of the nature of such a transition in terms of a) switch over from non-steady (in pure PP) to steady-state crack tip opening displacement rate (in nanocomposites), and b) a ductile-to-semiductile transition; largely as a result of delayed-yielding of the nanocomposites.