A multiplexing circuit and a mobile terminal, related to the field of electronic and communications technologies, that resolve a problem that product costs are high when a mobile phone uses an integrated switch. In the multiplexing circuit, a first switch circuit transmits, to a first signal transmission end, a right sound channel audio signal provided by a right sound channel transmission end. A second switch circuit transmits, to a second signal transmission end, a left sound channel audio signal provided by a left sound channel transmission end. Signal transmission between the first signal transmission end and a first output end and signal transmission between the second signal transmission end and a second output end are implemented by using a third switch circuit. The first switch circuit includes a first transistor and a first constant voltage control circuit.