© 2016 IEEE. Nonreciprocal spin wave propagation, induced by placing a neighboring metallic nonmagnetic layer, has been studied in metallic ferromagnetic thin films. The structure consists of a set of coupled microstrip transmission lines acting as antennas placed over a thin Ni80Fe20 layer. Nonreciprocal propagation of magnetostatic surface waves (MSSWs) has been observed. The nonreciprocal effect is evaluated by the amplitude ratio and the phase difference of the MSSWs traveling in opposite directions. By investigating the correlation between the device structure and the nonreciprocal effects, a maximum of -26.0 dB of the amplitude ratio and -180.0° phase difference were obtained. These results can be applied to optimize the nonreciprocal device.