Provided is a multi-channel optical subassembly. The multi-channel optical subassembly includes a first sub-mount including first and second areas having different thicknesses, a photoelectric device provided in the first area, a circuit board provided in the second area, a second sub-mount inserted into and fastened to the first guide hole and coupled to the first sub-mount, an optical fiber array fixed to the second sub-mount to provide a path through which light emitted from the photoelectric device is received or transferred, and a micro-lens array mounted on the second sub-mount. The first guide hole is provided in one of the first and second areas. The micro-lens array includes a lens collecting the light between the photoelectric device and the optical fiber array.