A bidirectional signal conversion circuit is configured to perform a signal conversion between a first port and a second port, and includes a switch, a first pull-up resistor, a second pull-up resistor, a first output-response enhancement circuit, and a second output-response enhancement circuit. The switch is coupled between the first port and the second port, and operates according to a bias. The first (second) pull-up resistor is coupled between the first (second) port and a high (low) voltage terminal having a high (low) voltage. The first (second) output-response enhancement circuit includes a first (second) alternative-current (AC) coupling circuit and a first (second) output-stage circuit. When the first (second) port and the second (first) port functions as an input port and an output port respectively, the first (second) output-response enhancement circuit is operable to accelerate the transient response of the output port.