This paper addresses the necessity of integration between buyer and suppliers for effective implementation of Just-In-Time purchasing in a multi-item environment. An integrated inventory model of facilitating multiple shipments in small lots is developed. Also, an iterative solution procedure is developed to simultaneously find the order(contract) interval for each item and number of shipments between buyer and suppliers. We show by example that when the integrated policy is adopted by both buyer and suppliers in a cooperative manner, both parties can benefit.