Scheduling is the allocation of resources over time to perform a collection of task. It is an important subject of production and operations management area. For most of scheduling problems made so far, the processing times of each job on each machine and due dates have been assigned as a real number. However in the real world, information is often ambiguous or imprecise. In this paper fuzzy concept are applied to the flow shop scheduling problems. The branch-and-bound algorithm of Ignall and Schrage was modified and rewritten for three-machine flow shop problems with fuzzy processing time. Fuzzy arithmetic on fuzzy numbers is used to determine the minimum completion time (C-max). Proposed algorithm gets a scheduling result with a membership function for the final completion time. With this membership function determined, a wider point of view is provided for the manager about the optimal schedule.