Among the variety of polyolefin conversion techniques, the biaxially oriented polypropylene (BOPP) manufacturing process is particularly demanding. A two-stage procedure transforms a casted polypropylene sheet (thickness 200-500 µm) into a thin (3-6µm) film of high crystallinity and stiffness. The polymer is subjected to a large strain plastic drawing in the partially molten state, requiring suitable rheological and thermal properties of the polymer. This study reports on effects of polymer structure on the biaxial drawing behavior of several propylene-ethylene random copolymers (PPR) and isotactic propylene homo polymers (PPH), tested with a laboratory scale biaxial orientation device. Casted sheets of the polymers were subjected to a simultaneous and equibiaxial drawing step at different drawing temperatures below the peak melting temperature of the polymers, using a commercially relevant strain rate. Engineering and true stress strain curves were obtained. The rheology of the post yield deformation phase was analyzed by fitting the true stress strain curves with two different constitutive models, to extract the network modulus GN of the partially molten material. It was found that close to the melting point, the biaxial drawing behavior is reasonable described as rubber-like, with good agreement between experimental data and simulated curves. Both models delivered similar values for GN. Irrespective of comonomer content, isotacticity or original crystallinity of the casted sheet, a plot of GN over relative drawing temperature collapsed most data to one relationship. In contrast, a pronounced high molecular weight fraction or a branched chain structure increased GN. However, both correlations converged at a GN of 0.1MPa, for drawing of nearly fully molten material. The results of this study confirm molecular effects on post yield behavior of the BOPP process, illustrating rheological aspects of BOPP processability to be relevant, in addition to melting behavior.