As-deposited Bi 2Sr 2CaCu 2O x films on (001) SrTiO 3 substrates produced by laser deposition are investigated in a high-resolution electron microscope. The films are well-oriented with the crystallographic c-axis and a-axis direction of the films parallel to the  and  direction of the substrate, respectively. The substrate/film interface is sharp and good crystalline order is build up from the interface. Misfit dislocations were found inside the film nearby the interface. Planar defects occur in the films. In particular, 90°-rotation twins are found with the rotation axis parallel to the c-axis. The growth mechanism of the films and the effect of the lattice defects on flux pinning is discussed.