Due to the increased demands for distribution/redistribution, recycling and repacking, there has been a significant change in the logistics process. This article presented an Ant Colony System (ACS) algorithm to solve a Vehicle Routing Problem with Simultaneous Delivery and Pickup (VRPSDP). The objective of this problem is to determine the optimal set of routes to totally satisfy both the delivery and pickup demand of the customer population. To solve the VRPSDP model, ACS approach is based in the pheromone strategy, inspired in the natural Ants behavior. This behavior is assigned to vehicles, which move along the route on which the pheromone intensity is strong. The ACS algorithm provides good solutions and shows that it is a competitive method related with other heuristics or meta-heuristics that have been proposed in literature.