This paper is concerned with the development of an inventory model for both ameliorating and deteriorating items. Generally it can be seen with the items such as broiler, duck, pig etc. when these items are kept in the farm or in the sales counter, they will increase in value due to their growth and decrease in value due to feeding expenses and /or diseases. Here in this paper an inventory model for above types of items with constant demand rate, without shortage and under influence of inflation and time-value of money is considered. Also the model is studied for minimization of total average cost if some extra inventory is added into or removed out of the lot. This paper investigates the optimal time for addition or removal of inventories so that the average cost will be minimum. The result is illustrated with numerical example.