An optical sensing module, including a frame, a light sensing element, and a diffusion element is provided. The light sensing element is disposed on the frame. The diffusion element is connected to the frame and is disposed above the light sensing element. In a first sensing mode, ambient light passes through the diffusion element before received by the light sensing element to make the optical sensing module to obtain light intensity of the ambient light. In a second sensing mode, the optical sensing module rotates around a first rotation axis to make the light sensing element face a display surface of the display device for receiving image light of the display surface so that the optical sensing module obtains brightness or chromaticity of the display device. A display device having this optical sensing module is also provided.