A diffusion unit of a light-emitting module is disposed adjacent to at least one light source. The light source emits a light beam. The diffusion unit includes a first diffusion sheet and a second diffusion sheet. The thickness of the first diffusion sheet is less than 1 mm, and the thickness of the second diffusion sheet is also less than 1 mm. The second diffusion sheet is disposed adjacent to the first diffusion sheet. The light beam is directly emitted from the light source directly to the first diffusion sheet. A light-emitting module and a diffusion sheet are also disclosed.