Polymers from industrial byproducts and waste streams show great potential as low-cost biomaterial resources. Novatein Thermoplastic Protein (NTP) is a bio-derived alternative for fossil-fuel based plastic products. Its main component is dried bovine blood which is a low value by-product from the meat processing industry and is at least 90 % protein. Rheological properties, such as shear and extensional viscosity, are critical in defining polymer's thermo mechanical processability properties. In comparison to conventional polymers, extensional viscosity of protein plastics is typically drastically higher. Thus, applications of more advanced processing methods such as sheet extrusion and injection molding are limited. In this study, extruder driven capillary rheometer was used to determine rheological properties and its modification possibilities of NTP. Pressure requirements for different mass flow rates were collected by using three different length capillaries and these values were used to calculate true shear stress, shear rate and viscosity values by using Bagley and Rabinowitsch corrections. Extensional viscosity properties were calculated from the entrance effect properties. Aim of the study is to determine the effect of different plasticizers and understand which of the processing parameters affects extensional properties the most.