Abstract: This paper deals with the problem of determining the firm's optimal marketing investment level and ordering policies simultaneously for deteriorating items under the condition of permissible delay in payments,in order to maximize its annual net profit.In this article we develop an algorithm to solve this problem.Also,the effect of sensitivity of demand on marketing investment,credit period length and deteriorating rate on the firm's optimal strategy and profit is examined.

Key words: deteriorating products, delay in payments, ordering policy, marketing decision