We consider the closed orientable hypersurfaces in a wide class of warped product manifolds, which include space forms, deSitter-Schwarzschild and Reissner-Nordström manifolds. By using an integral formula or Brendle’s Heintze-Karcher type inequality, we present some new characterizations umbilic hypersurfaces. These results can be viewed as generalizations classical Jellet-Liebmann theorem Ale...