Transmission electron microscopy (TEM), energy dispersive analysis of x ray (EDS), x-ray diffraction, electrical resistance, and magnetic susceptibility measurements were applied to characterize the structure and microstructures of a high-Tc superconducting YBaSrCu3O7-δ compound. The sintered samples were found to be predominantly of a single phase with a modified perovskite structure. Combined EDS/TEM and high-resolution lattice imaging with computed image simulation data showed that the atomic ratio of Sr and Ba atoms is about unity and Ba sites in YBa2Cu 3O7-δ compound were partially substituted by Sr atoms in the three-layer perovskite structure, in agreement with the results of a previous neutron diffraction study. It was also found that the marked contrast difference in high-resolution images along  and  directions of the high-Tc oxygen-deficient superconducting crystals can be used to advantage to distinguish  and  directions of the modified perovskite structure in TEM. Lattice defects such as twins and dislocations were observed and analyzed.