The rheological behavior of ultrahigh molecular weight polyethylene (UHMWPE) semidilute solutions with different solvents has been studied. In a temperature range of 150–185°C, the viscosity of a UHMWPE semidilute solution with paraffin oil as solvent (soln 1) is more temperature-independent and viscosity-stable than that with decalin as solvent (soln 2). Usually the reduction of the molecular entanglement density in solution causes a rapid reduction in viscosity. Apparently soln 1 has a different entanglement density compared with soln 2. The activation energy of UHMWPE semidilute solutions changes with both shear stress and shear rate. The regressive equations for both solutions in between Eσ and σ or E and equation image have been obtained from a least-squares method. Finally, there is a discontinuity in the non-Newtonian flow region of η vs. equation image curve, no matter which temperature or solvent was used. The discontinuity occurs at a shear rate of about 70 s−1, where a transformation from a qualitative change in entanglement in the solution takes place.