Multi-layered MoS2 (or WS2) nanocages stuffed with Mo (or CoS/CoO) nanocrystals have been synthesized by using the reaction between metal nanoparticles and sulfur powders. This simple synthesis method, different from the conventional methods for synthesizing pure inorganic fullerenes, is also potentially important for large-scale synthesis of nanoparticles of other metal dichalcogenide. Besides the multi-layered WS2 nanocapsules, we have successfully fabricated nanocapsules with a single-layered WS2 sheet encapsulating W by using the arc-discharge method. We discuss possible mechanisms for the formation of the unique core-shell structured nanocapsules. (c) 2005 Springer Science + Business Media, Inc.