The dependence of shear and elongational viscosity on the molecular weight of poly(vinylidene fluoride) has been studied using a capillary rheometer, The elongational viscosity was evaluated based on Cogswell＇s method with two types of capillaries: capillary length (L)/capillary diameter (D) = 10 mm/1 mm and LID = 0 mm/1 mm. We used the ratio P-0/P-L that indicates the contribution of elongational flow to the total flow involving both the shear and elongational flows. P-L and P-0 are the pressure losses in the capillary and the converging flows, respectively. P-0/P-L increased with molecular weight and shear rate. This corresponds to decreasing the number of entanglements of molecular chain under a large displacement, especially high shear. Thus, we suggest using P-0/P-L as the parameter of the entanglement interaction on the molecular chain under a large displacement.