The structure development of beta nucleated polypropylene (iPP) during extension induced crystallization was studied by in-situ synchrotron X-ray scattering.Wide angle X-ray scattering (WAXS) results indicated that the beta crystals grew epitaxially on the lateral surface of oriented needle-like beta nucleating agent and formed cuboid-like crystalline lamellae.Small angle X-ray scattering (SAXS) revealed that the oriented beta lamellae and shish-kebab structure developed simultaneously during the extension induced crystallization.