In this paper, we have demonstrated a 1×3 wavelength multiplexer/demultiplexer using optical MEMS technology based on a Gires-Tournois interferometer (GTI) with a tunable center wavelength. The center wavelength of each output port was continuously tunable across the free spectral range, and, the output port assignment can therefore be cyclically interchanged. These types of wavelength tunability and port reallocation offer useful functionality in various WDM systems.