  We elaborate the renormalization process of entropy of a nonextremal and an
extremal Reissner-Nordstr\"{o}m black hole by using the Pauli-Villars
regularization method, in which the regulator fields obey either the
Bose-Einstein or Fermi-Dirac distribution depending on their spin-statistics.
The black hole entropy involves only two renormalization constants. We also
discuss the entropy and temperature of the extremal black hole.
