An optical sheet includes a transparent base, a plurality of first micro structures, and a plurality of second micro structures. The transparent base has a light-receiving surface and a light-exit surface. The first micro structures are disposed on the light-exit surface, and the second micro structures are disposed on the light-receiving surface. Each first micro structure includes a first planar surface and a curve surface. Each second micro structure includes a second planar surface formed on the light-receiving surface and a total reflection surface connected with the second planar surface. Each first micro structure forms a first orthogonal projection area on the light-receiving surface, each second micro structure forms a second orthogonal projection area on the light-receiving surface, the second planar surface is located within the first orthogonal projection area, and the entire area of the second planar surface is equal to the second orthogonal projection area.