Recently, two-dimensional(2D) layered molybdenum disulfide(Mo S_2) has attracted great attention because of its graphene-like structure and unique physical and chemical properties. In this paper, physical structure, band gap structure, and optical properties of Mo S_2 are summarized. Mo S_2 is semiconducting and composed of covalently bonded sheets held together by weak van der Waals force. In each Mo S_2 layer, a layer of molybdenum(Mo) atoms is sandwiched between two layers of sulfur(S) atoms. There are t...