Abstract: In Ref [1] the asymptotic stability of nonlinear slowly changing system has been discussed.In Ref [2] the instability of solution for the order linear differential equaiton with varied coefficient has been discussed.In this paper,we have discussed instability of solution for a class of the third order nonlinear diffeential equation by means of the metod of Refs [1] and [2].

Key words: ordinary difterential, cquation motive stability theory, nonlinear differential equation