It has been recognized that rheological responses under elongational flow affect the processability greatly at various processing operations. Therefore, numerous efforts have been carried out to control the elongational viscosity. The evaluation of the rheological responses under uniaxial elongational flow is, however, often carried out by measuring the force required to stretch a molten polymer after passing through a die, which is defined as drawdown force. The drawdown force is known to be greatly enhanced by the addition of rigid fibers by the excess shear deformation of a matrix between fibers, although the system does not show marked strain-hardening behavior in transient elongational viscosity. Furthermore, the crystallization behavior plays an important role on the drawdown force for a crystalline polymer, because it is evaluated at the non-isothermal condition. For example, the drawdown force of isotactic polypropylene (PP) and high-density polyethylene (HDPE) is found to be sensitive to the length of dies. This is attributed to the prompt crystallization of a polymer melt with fewer entanglement couplings by the exposure to the prolonged shear stress in a long die, which provides the steep increase in the elongational force. Therefore, the drawdown force can be enhanced by the addition of a nucleating agent, which is proved using PP. Finally, the addition of a small amount of poly(methyl methacrylate) (PMMA) with low molecular weight is found to enhance the drawdown force of PP. Because of the very fast cooling rate at the drawdown force measurement, the solidification of PMMA occurs faster than the crystallization of PP. Consequently, deformed PMMA domains act as rigid fibers in the PP melt, leading to the enhancement of the drawdown force.