In this paper, we study the long wave approximation for quasilinearsymmetric hyperbolic systems. Using the technics developed byJoly-Métivier-Rauch for nonlinear geometrical optics, we prove thatunder suitable assumptions the long wave limit is described byKdV-type systems. The error estimate if the system is coupled appears tobe better. We apply formally our technics to Euler equations with freesurface and Euler-Poisson systems. This leads to new systems of KdV-type.