Bi-Sr-Co-O oxide semiconductor system has a typical misfit-layered crystal structure and a promising thermoelectric property. There are two different kinds of electron diffraction patterns taken with the electron beam parallel to the c-axis. Monoclinic unit cell was defined for the system having the metal ratio close to Bi:Sr:Co∼1:1:1 by Leligny et al.1) The metal ratio of the present crystal is Bi:Sr:Co∼1:0.8:1.1, being Co-rich and Sr-poor. The ratio was determined using an electron probe microanalyer. Oxygen content was determined by the inert gas-carrier fusion-infrared absorption method. Triclinic unit cell is determined by means of the whole pattern fitting technique, i.e., the Le Bail decomposition method, based on the neutron and X-ray power diffraction patterns, using a powder diffraction pattern fitting program Jana2000.2) There are chemical content dependent changes in the structural parameters. The lattice parameters are typically a,b 1(RS),b2(CoO2),c,α,β,γ =4.94Å, 5.26Å, 5.45Å, 15.21Å, 90.2°, 93.8°, 89.3°, respectively.