Electronic Journal of Differential Equations, Vol. 2011 (2011), No. 60, pp. 1-9. Title: Optimization problems involving Poisson's equation in R^3 Authors: Fariba Bahrami (Univ. of Tabriz, Iran) Hossain Fazli (Univ. of Tabriz, Iran) Abstract: In this article, we prove the existence of minimizers for integrals associated with a second-order elliptic problem. For this three-dimensional optimization problem, the admissible set is a rearrangement class of a given function. Submitted February 16, 2011. Published May 10, 2011. Math Subject Classifications: 49J20, 49K20. Key Words: Rearrangements class; variational problem; Poisson's equation; energy functional; minimization.