Abstract: Self-focusing of whistler waves in the magnetosphere are analysed. The results show that it is possible for moderate and strong whistlers to be focused during their propagation in the magnetosphere. The self-focusing may be a nonlinear mechanism for the guided propagation of the whistlers. Furthermore, it is pointed in this paper that, if there is wave amplification in the magnetosphere, it is easier for the waves to be focused ; oppositely, if there is wave absorption, it is not easier for the waves to be focused.