A HREM study on the defects in the high‐Tc superconductor YBaCuO discovered recently is reported. It is found that there are large amounts of local lattice distortions, point defects, and misarrangements of Y or Ba atoms within the specimens observed. HREM images of grain boundaries and interfaces between the crystalline state and so‐called intermediate‐ordered state are obtained. It is found that the tripled period lattices are distorted, especially near the interfaces.