The micromechanical deformation behaviour of lamellar styrene/butadiene block copolymers crosslinked by gamma-irradiation was studied by transmission electron microscopy and scanning electron microscopy. Irrespective of the irradiation dosage, the micromechanical mechanism in these samples is predominantly necking and drawing of glassy lamellae accompanied by shearing in the rubbery phase. However, the samples behave in a brittle fashion at higher irradiation dosages, which is associated with the surface damage caused by gamma-irradiation.