A novel design of an all-optical switch is proposed based on a nonlinear photonic crystal Mach-Zehnder interferometer (PC-MZI) to get the maximum switching speed and the minimum consuming power. As far as we know, this is the first study using a nonlinear polymer in one of the PC-MZI arms for realizing the switching phenomenon. All used components, such as bends, waveguides, and splitters, were individually optimized. Finite difference time domain and plane wave expansion methods were also utilized for the simulation of light propagation in the proposed structures.