This paper deals with an optimal method for solving a 2-stage flexible flow shop scheduling problem with group constraint, batch released dates. This problem is known to be NP-hard. In this paper, first of all, we construct a mathematical model for the problem. Then, we develop a branch and bound method with heuristic algorithm for the optimal solution of the problem. During the initialization, we use a heuristic algorithm H’ as the initial solution. We propose two branching algorithms in the branching procedure and two algorithms for the lower bound. We also propose a set of instances for this type of problem. The results are shown that our branch and bound method is effective for small and medium-sized problem but large-sized problem.