The design of a supply chain has been considered by many practitioners and researchers recently. One model that is used to optimize distribution from a single facility (depot) to a set of retailers over a given planning horizon and considering stock management decisions is known as Inventory Routing Problem (IRP). This model tries to optimize the trade-off between inventory and transportation costs. Designing IRP becomes more complex if the items are deteriorating. In this research, we develop IRP for deteriorating items where there is possibility that every vehicle has more than one route. Multi routing is suitable for deteriorating items since it minimizes delivery time for each item. We consider more than one vehicle at the depot and each vehicle has similar maximum capacity. Since the problem is an NP hard problem, we use Particle Swarm Optimization (PSO) method to solve the problem. A numerical example and sensitivity analysis are conducted to show the deteriorating rate effects at the vehicle and inventory, and also inventory and transportation cost to the total supply chain cost. The results show that the total cost/hour is more sensitive to different values inventory deteriorating rate than transportation deteriorating rate.