Electronic Journal of Differential Equations, Vol. 2005(2005), No. 129, pp. 1-11. Title: An application of the Lyapunov-Schmidt method to semilinear elliptic problems Author: Quoc Anh Ngo (Vietnam National Univ., Hanoi, Vietnam) Abstract: In this paper we consider the existence of nonzero solutions for the undecoupling elliptic system $$\displaylines{ -\Delta u=\lambda u+\delta v+f(u,v), \cr -\Delta v=\theta u+ \gamma v+g(u,v), }$$ on a bounded domain of $\mathbb{R}^n$, with zero Dirichlet boundary conditions. We use the Lyapunov-Schmidt method and the fixed-point principle. Submitted July 12, 2005. Published November 23, 2005. Math Subject Classifications: 35J50, 35J55. Key Words: Semilinear; elliptic system; Lyapunov; Schmidt; fixed-point principle.