In today’s busy life, no one has sufficient time to buy or bargain any type of products. It is common in such cases that customers, who are looking for purchasing a certain product, will be willing to substitute with a comparable product when facing a stock-out, rather than visiting a different store to bargain the original product. In this article, we study an inventory control problem in which demand is fulfilled by using two similar substitutable items. Retailer fulfilled demand of one product by other substitutable product when stock-out of the one of them. We consider inventory levels of both of the items and time dependent demand. The orders for both products are placed at the same time. Our objective is to maximize joint profit for two substitutable deteriorating items with respect to cycle time and a time at which one product is stock-out.The numerical analysis is carried out based on the analytical results. The critical inventory parameters are computed for the decision maker.