Abstract Bi-Sr-Ca-Cu-O thin films grown on (001) MgO substrates by chemical vapor deposition with T c at 110 K have been evaluated by transmission electron microscopy. From plan-view observations, the films are found to consist of large domains oriented along the c axis, with diameters of 15-100 μm. These domains exhibit incommensurate superstructures along the b axis. In addition, we have observed similar superstructure spots elongating in two equivalent directions normal to each other. Cross-sectional observation has indicated that the interface between the Bi-Sr-Ca-Cu-O thin film and the substrate is very abrupt. Five different perovskite-related layers along the c axis, with different thickness are successfully observed. In the thin film, 80 K phases with c = 3.0 nm are dominant and 110 K phases with c = 3.6 nm are less likely, which is very consistent with the results from X-ray diffraction. Three other phases are very rarely observed. Furthermore, boundaries where the layered structure is different on both sides are often found.