The development of devices for communication networks to transmit information has become an active and growing field of research. Multiplexer/demultiplexer (M/D) is one of the basic devices in this field. In this paper, an M/D design is introduced based on the surface plasmon resonance in optical ring resonators. The number of inputs and outputs of M/D is 3 × 1 and 1 × 3, respectively. All parameters of the structure, including radius and width of ring resonators and waveguides, have been evaluated to obtain the optimal response. Also, we used the nonlinear gold property to expand the range of M/D performance and simulated the results for intensities less than 100 MW/cm2. Selectivity in the number of inputs and outputs, controllability using several parameters, all optically, selectivity in operation frequency, nanoscale size, reconfigurability, and integrated capability are the features of this design. In our simulation, we consider transmission and reflection of light in each port based on the finite difference time domain for evaluation of results.