In some companies, undesirable costs are imposed for provision of services. It is required that current outputs of decision making units are produced at minimal undesirable cost. In this paper, a new method is proposed for evaluating the undesirable cost imposed on the units. Moreover, data is considered in fuzzy number form, due to the observed input-output data are sometimes imprecise in real applications. Applying the -level based approach, the proposed mode is solved to measure minimum undesirable cost. In this method, data information is supposed as triangular fuzzy numbers. Finally, the proposed method is illustrated by a real application. تفاصيل المقالة