Abstract By means of the first-principles calculations, we studied the density of states, band structure and Fermi surface nesting of the recently discovered BiS2 layered superconductor LaO1−xFxBiS2. At x=0, the density of state and band structure of LaOBiS2 indicate the compound is a insulator with a band gap of 0.15eV. It becomes metal with F-doping. At x=0.5, there are four bands crossing the Fermi level. These four bands are mostly derived from the Px and Py orbitals of Bi atoms. Compared with the typical Fe–As based superconductor LaOFeAs, the Fermi surface nesting of LaO1−xFxBiS2 is not as strong as that of LaOFeAs.