Abstract: The nonlinear dispersion relation of an elliptically polarized laser pulse in plasmas was derived by means of Lorentz technique.The modulation instability with finite amplitude in plasmas was analyzed on the basis of the nonlinear controlling equation for transverse wave.The temporal growth rate as a function of perturbed wave number for laser beam propagating through plasmas was found analytically and the modulation instability growth rates in the different regions of plasmas were compared, It is shown that the temporal growth rate of modulation instability is increased significantly in the corona region near the critical surface in laser-produced plasmas.