An optical transceiver installed with a replaceable transmitting module, comprising: a casing; a circuit board, disposed within the casing; an optical receiving module, connected with the circuit board, the optical receiving module comprising a plurality of photo diodes or a photo diode array consisting of a plurality of photo diodes, a first cover disposed on the photo diodes respectively or disposed on the photo diode array, and one or more first lenses disposed on the first cover and corresponding to the photo diodes respectively, and a flexible PCB connected to the photo diode and the circuit board; the replaceable transmitting module, disposed on the casing and connected with the circuit board, the replaceable transmitting module comprising a plurality of optical sub-assemblies disposed independently respectively, and at least one positioning mount disposed on the casing,each of the optical sub-assemblies comprising one edge-emitting laser diode, a second cover disposed on the edge-emitting laser diode, a second lens disposed on the second cover and corresponding to the edge-emitting laser diode, and a flexible PCB connected to the edge-emitting laser diode and extended from a rear side of the optical sub-assemblies to the circuit board to electrically connect the edge-emitting laser diode and the circuit board, and the positioning mount comprising a base, and a plurality of positioning portions disposed on the base and fixing the optical sub-assemblies, respectively; and a connector, connected to the optical receiving module and the replaceable transmitting module to receive and transmit an optical signal; wherein the optical receiving module and the replaceable transmitting module directly stack up with each other, and the flexible PCB of the optical receiving module and the flexible PCB of the replaceable transmitting module connect to the front and the back of the circuit board individually. a casing; a circuit board, disposed within the casing; an optical receiving module, connected with the circuit board, the optical receiving module comprising a plurality of photo diodes or a photo diode array consisting of a plurality of photo diodes, a first cover disposed on the photo diodes respectively or disposed on the photo diode array, and one or more first lenses disposed on the first cover and corresponding to the photo diodes respectively, and a flexible PCB connected to the photo diode and the circuit board; the replaceable transmitting module, disposed on the casing and connected with the circuit board, the replaceable transmitting module comprising a plurality of optical sub-assemblies disposed independently respectively, and at least one positioning mount disposed on the casing,each of the optical sub-assemblies comprising one edge-emitting laser diode, a second cover disposed on the edge-emitting laser diode, a second lens disposed on the second cover and corresponding to the edge-emitting laser diode, and a flexible PCB connected to the edge-emitting laser diode and extended from a rear side of the optical sub-assemblies to the circuit board to electrically connect the edge-emitting laser diode and the circuit board, and the positioning mount comprising a base, and a plurality of positioning portions disposed on the base and fixing the optical sub-assemblies, respectively; and a connector, connected to the optical receiving module and the replaceable transmitting module to receive and transmit an optical signal; wherein the optical receiving module and the replaceable transmitting module directly stack up with each other, and the flexible PCB of the optical receiving module and the flexible PCB of the replaceable transmitting module connect to the front and the back of the circuit board individually.