Abstract: The effect of a longitudinal electric field on whistlers is studied based on kinetic theory. A local Maxwellian distribution is taken as steady distribution function of electrons which departs from equilibrium due to the applied electric field. The dielectric tensor is derived by integrating along orbits of the particles in the unperturbed field. Dispersion relation and growth rate are analyzed from Hermitian and anti-Hermtian part of this tensor respectively. It is found that the waves are growing when the angle between wave vector and electric field is in the range of c, otherwise the whistler waves are damping. The growth rate increases with the wave frequency and decreases with the angle between wave vector and applied field. In case ee, the maximum of growth rate, which is at =0, is proportional to the plasma density and anti-proportional to the magnetic field intensity. Some computed results for parameters at top of F layer are given.