In this paper two global optimization methods are applied to the separation network synthesis (SNS) problem. The first is a stochastic method of CSENDES [1], the second is an interval method. The latter method used is a two-stage algorithm where in the first stage a close upper bound for the global optimum is given. The efficiency of these methods is illustrated by solving the SNS problems given by FRIEDLER et al. [2] and KOVACS et al.[3].