The flexibility in manufacturing environment is implemented to respond proactively and cost effectively towards dynamic production requirements. Previous literature has explored eight common types of flexibility in manufacturing. This paper presents a simulation study based on Part-mix and Routing Flexibility and their impact on system performance of a typical Flexible Manufacturing System (FMS). ARENA based computer simulation models have been developed to investigate the effect of flexibility on the performance under various control strategies (sequencing and dispatching rules). The performance measure used in this paper is make-span time. Unbalanced type job shop FMS consist of four CNC general purpose machining centers and one loading/ unloading station is considered for the illustration of simulation models. These demo simulation models are intended for deterministic environment, and the use of discrete event simulation approach is adopted to offer a focus on dynamic behavior of FMS operating under different manufacturing strategies and flexibility types. This simulation study, under dynamic environment, may be very useful for practitioners. Management can obtain better insight and guidelines for determining various decisions relating to process and operations improvement and investment in new facility.