© 1980-2012 IEEE. Excitation of non-reciprocal magnetostatic surface wave (MSSW) has been studied in an ultra-thin yttrium iron garnet (YIG) film. The YIG films were grown on a gadolinium gallium garnet (111) substrate using pulsed laser deposition. The films exhibit an exceptional crystalline quality and an extremely low magnetic damping at radio frequency and microwave. Non-reciprocal MSSWs in a 20-nm-thick YIG film has been observed using a coupled coplanar waveguide structure with a shared common ground. Increase of the YIG film thickness to 190 nm, the non-reciprocity has been significantly enhanced, resulting in a maximum 10-dB amplitude gain and 55.5° phase shift in 30-mT magnetic field between the MSSWs traveling in opposite directions. In the absence of magnetic field, the device shows a reduced amplitude gain of 2 dB and a phase shift of 15.8°. These results can find broad applications in building self-biased spin-wave-based components in integrated signal processing and communication system.