Surface structures of the high‐Tcsuperconductor YBa2Cu3Oxhave been investigated with a scanning tunneling microscope. Four typical features are revealed, e.g., (i) flat area of the size up to 0.2×0.2 &mgr;m2, (ii) step structures with the height of the step from tens to hundreds of angstroms, (iii) regular arrays of subgrains having the width down to 100 A˚, and (iv) a complex formed by these features. The sharp surface corrugations suggest strong local fluctuations in the elastic and electronic properties of this material.