An S-band GaAs Field Effect Tube(FET) microwave bi-directional circuit is designed as a power amplifier and a rectifier. The similarity between a power amplifier and a rectifier is discussed. The circuit is simulated by ADS and measured. In the amplifying mode, the circuit receives a high DC-MWPAE(Power Added Efficiency) as 55% with an output power of 28.9 dBm and a gain of 11.9 dB. The circuit is able to work in rectifying mode as well. It is biased in the class-C mode and shows an efficiency of 75.6% as the microwave input power is 30 dBm with a DC load of 55 Ω. The characteristics that the circuit can be an amplifier forward and a rectifier reverse would be applied to the bi-directional system of microwave wireless power transmissions.