Nd-Ba-Cu-O high Tc superconductor is studied with electron diffraction and high resolution electron microscopy. The main phase is orthrombic with distorted perovskite structure. The lattice parameters are a = 3.84?, b = 3.87?, c= 11.7?. There are many defects in the sample. Edge dislocations and anti-phase domains are observed by lattice imaging. The structure mode) of NdBa2Cu3O7-δ is determined from the structure image. Depending on the imaging conditions either the heavy atoms or oxygen atoms appear as white dots in the high resolution electron microscope images. The oxygen atoms can be distinguished from the vacancies in the image under a suitable imaging condition.