Atomic structure of a natural molybdenite (MoS2) single crystal basal plane was examined by ultra-high vacuum scanning tunneling microscopy (UHV-STM). Numbers of crater structures with diameters ranging from 5 to 9 nm were observed on pristine as well as on high-temperature (473 K) resulfided surfaces. Atomic structures within these craters were continuous from the surrounding terrace, with no step structures at the rims of the craters. Atoms in the bottom of the craters showed higher corrugations compared to the terrace atoms, indicating higher electronic density of states in the craters. Its implication on hydrotreating activity over curved MoS2 nanoparticles is discussed. (C) 2004 Elsevier B.V. All rights reserved.