Abstract: Self-focusing of whistler waves due to ponderomotive force has been analysed in this paper.The general results have been used to see the possibility of self-focusing of whistlers in the earth magnetosphere.The results show that,for moderate and intense whistlers (the wave electric field>～1mV/m),the self-focusing is possible.Therefore,it may be a nonlinear mechanism for the ducted propagation of such whistlers in the magnetosphere.