An optical structure of the optical mouse is disclosed, which comprises a light source providing an incident light beam transmitted onto a target surface at a specific incident angle and a photosensor pre-disposed at an angle of between 1 and 179 degrees or between 181 and 359 degrees so as to be aligned to stand at a right angle with respect to a path of the reflected version and thus achieve a proper acquirement of luminance and image of the reflected version of the incident light from the target surface.