The morphology of polymers is strongly determinded by the thermal and flow history of the melt. To understand the development of the morphology and its changes during deformation of beta nucleated polypropylene in-situ investigations by synchrotron wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) were performed. Samples with defined thermomechanical history were stretched at elevated temperatures in a range from 60 °C to 120 °C and with stretching rates from 0.1 to 1.5 mm/s. The changes in the morphology were monitored and its influence on the mechanical properties were discussed.