Micro- and meso-scale structure changes of -form isotactic polypropylene (-iPP) during uniaxial stretching is studied by time-resolved synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The structure/property relations are investigated at different temperatures, and the effects of isothermal crystallization are also studied with POM. The X-ray scattering results show that the long period increased and the lamellar oriented along the stretching direction in the elastic deformation stage. The lamellar and crystals start destructing after yielding. And from it POM images it can be seen that with higher crystallization temperature the spherulites connected to form a crystalline network, on which the stress is mainly loaded. It turns out different environment temperatures affect mostly the amorphous domains. And samples exhibit different yielding mechanisms with different thermal histories. A hypothetical structural mechanism is proposed based to explain the observed relationship between the processing parameters, thermal history and the structure/property relations of -iPP. POLYM. ENG. SCI., 58:160-169, 2018. (c) 2017 Society of Plastics Engineers