To understand the toughness enhancement of beta-nucleated isotactic polypropylene (iPP) in comparison with iPP, the differences in the micro-deformation mechanisms between the neat iPP and beta-nucleated iPP were visualized using the confocal laser scanning microscopy (CLSM). Structure of the alpha- and beta-spherulites situated close to the tip of the sharp starter crack has been investigated during tensile deformation in the viewing field of the CLSM. In the alpha-spherulite of the neat iPP, highly localized inter- and intra-spherulitic micro-shear bands have been observed. In the beta-nucleated iPP, relatively uniform distribution of diffuse shear bands has been observed in the beta-phase, while the alpha-phase remained relatively undeformed exhibiting only narrow intra-spherulitic shear bands in the direction perpendicular to the loading direction. Delocalization of plastic deformation into diffuse shear bands in beta-nucleated iPP can explain its enhanced crack resistance compared with the neat iPP exhibiting highly localized shear banding. POLYM. ENG. SCI., 51:2434-2438, 2011. (C) 2011 Society of Plastics Engineers