The blown film extrusion process is extensively used in the packaging industry to make large volumes of semi-crystalline polymer films. Due to the considerable amount of research dedicated to polymer processing in the last few decades (1), it has become well known that the conditions applied during the production process, together with the molecular features of the resin, determine in a large amount the final microstructure, mechanical and optical properties of the film. The final morphology of the blown film has been studied as function of processing conditions and material composition by means of numerous experimental methods (2-4). However, in these cases, measurements were carried out off-line on the final products and the optimal processing conditions could be determined only by trial and error, making the procedure time consuming and expensive. On-line measurements of the structure development by means of X-ray scattering techniques are the key requirement in order to fully understand the influence of processing conditions, such as blow-up and take-up ratio (BUR and TUR), and of molecular features such as long chain branching content (LCB) and molecular weight distribution (MWD). A blown film unit and extruder were installed on the DUBBLE beamline at the European Synchrotron Radiation Facility (ESRF-Grenoble, France). Since film-blowing is a stationary process, 2D small angle scattering patterns were recorded at different heights, ranging from the die exit to beyond the frost line, typically 15-20 cm above. Experiments were performed on 3 different materials (2 linear low density polyethylenes (LLDPE) with different amount of butyl branching and a blend of LLDPE with 10% of low density polyethylene) using 4 different sets of BUR and TUR. Using 1D autocorrelation function analysis of the SAXS patterns obtained we obtained the long period, linear crystallinity and lamellar thickness evolution along the bubble as a function of the processing variables. The orientation was also determined using the Herman orientation factor method. In this research, we used, for the first time, small-angle X-ray scattering (SAXS) to probe the evolution of lamellar thickness and molecular orientation, the main quantities governing mechanical properties, as function of both blow-up and take-up ratio for different material compositions.