The effects of polymer additives on the behavior of the kinetic energy spectrum in isotropic decaying turbulence were numerically investigated by hybrid Eulerian-Lagrangian simulations making full use of large-scale parallel computation. The kinetic energy spectrum was found to obey the power-law E(k) ~ k−α in the range below the Kolmogorov length lK when the turbulence decayed. The exponent α satisfied 4 < α < 5 and decreased with the increase in the Weissenberg number Wi. The value of α obtained by the largest Wi run was close to the values obtained in previous experimental and numerical studies on elastic turbulence, which is characterized by a larger Wi and a Reynolds number of less than unity. The relationship between the results of the present study and the results obtained for elastic turbulence is also discussed.