An optical sheet includes a base film in which light is incident from a lower side, a plurality of prism patterns and a diffusion member. The prism patterns are protruded to be spaced apart from each other on the base film to enhance the front luminance of light incident from the lower side of the base film. The diffusion member is disposed between prism patterns to have a diffusion surface in parallel with the base film. The diffusion member includes a plurality of diffusion dots capable of enhancing the luminance uniformity of light incident from the lower side of the base film. Thus, front luminance and luminance uniformity may be enhanced due to a juxtaposition of the prism patterns and the diffusion portion, and the viewing angle of the LCD device may be enhanced.