This study investigates the coordination of production scheduling and maintenance planning in theflow shop scheduling environment. The problem is considered in a bi-objective form, minimizing themakespan as the production scheduling criterion and minimizing the system unavailability as themaintenance planning criterion. The time interval between consecutive maintenance activities as well as thenumber of maintenance activities on each machine are assumed to be non-fixed. A mixed integerprogramming formulation of the problem is presented. A special case of the problem, named as single servermaintenance is also studied. Then, a bi-objective ant colony system algorithm is presented to solve theproblem in focus. To obtain the appropriate components of the proposed algorithm, two sets of experimentsare provided. Firstly, experiments are carried out to select the suitable heuristic method to build the heuristicinformation part of the algorithm between CDS and NEH. Secondly, experiments are reported to select thelocal search algorithm between iterated local search and adjacent pair-wise interchange. At last, experimentsare generated to evaluate the performance of the proposed algorithm, comparing it to the results of anexhaustive search algorithm.