Electronic Journal of Differential Equations, Vol. 2006(2006), No. 61, pp. 1-13. Title: Asymptotic behavior of solutions to a $2\times2$ reaction-diffusion system with a cross diffusion matrix on unbounded domains Author: Salah Badraoui (Univ. du 08 Mai 1945, Guelma, Algeria) Abstract: This article concerns the behavior at $\mp \infty $ of solutions to a reaction-diffusion system with a cross diffusion matrix on unbounded domains. We show that the solutions satisfy the free diffusion system for all positive time whenever the initial distribution has limits at $\mp \infty$. Submitted October 27, 2005. Published May 11, 2006. Math Subject Classifications: 35B40, 35B45, 35K55, 35K65. Key Words: Reaction-diffusion systems; analytic semi-group; local solution; cross diffusion matrix; unbounded domain; asymptotic behavior of solutions.