In this paper, a fuzzy inventory model for time-degenerating items using penalty cost under the conditions of infinite production rate is formulated and solved. Here, the penalty cost is assumed under two cases such as linear and exponential. The holding cost and setup cost and the demand rate are assumed to be fuzzy. In fuzzy environment all related parameters are assumed to be hexagonal. Representing these three costs by hexagonal fuzzy numbers, the optimum order quantity is calculated using signed distance method for defuzzification .Numerical examples have been given in order to show the applicability of the proposed model.