In this research, we used, for the first time, in-situ small-angle X-ray scattering (SAXS) to probe the evolution of lamellar thickness, linear crystallinity and molecular orientation, the main quantities governing mechanical properties, as function of both blow-up and take-up ratio for three different polyethylene grades (two LLDPE film blowing grades with different short side-chain branching content and one LLDPE blended with 10% of LDPE). The resulting films were then mechanically tested by stretching them in different orientations in respect to machine direction (MD) and final properties were related to the different processing conditions/ structure evolutions.