The influence of morphology on micromechanical deformation behaviour of blends consisting of a lamellar forming styrene/butadiene star block copolymer and polystyrene homopolymer (hPS) was studied by transmission electron microscopy (TEM). The pure star block copolymer and the microphase separated blends revealing lamellar structure with polystyrene (PS) lamella thickness in the range of about 20 nm showed homogeneous plastic deformation of the PS lamellae. The macrophase separated blends with PS particles in lamellar matrix exhibited debonding at the particle-matrix interface associated with extensive plastic deformation of the surrounding matrix. The blends containing PS matrix deformed via crazing. (C) 2003 Elsevier Ltd. All rights reserved.