This paper considers the production/inventory model of a system in which inventory facilities are in series and between them are production/assembly units. There are inventory stocks for raw material, in-process products and end-product. External demand for an end-product is placed at the end-stock point in the system. It is assumed that uncertainty appears in external demand. Uncertainty is propagated along the production/inventory system. Modeling of the external disc rate imprecise demand is based on fuzzy sets.