By using Lyapunov functions, we obtain, for the first time, necessary and sufficient conditions for the exponential stability of some nonlinear systems of differential and difference equations.In the present paper, we obtain necessary and sufficient conditions for the global exponential stability and exponential instability for one class of nonlinear systems of differential and difference equations. We investigate the exponential stability of perturbed systems with nonlinear first approximation.Note that the problem of the exponential stability of nonlinear systems is connected with the work by Grujic [1], in which sufficient conditions were obtained for the global exponential stability of one nonlinear complicated system with nonlinear isolated subsystems, which are assumed to be either exponentially stable or exponentially unstable.