BaXO4 (X=Mo, W) manobelts and a variety of hierachical supersructures assembled from the nanobelts have been synthe-sized I na catanionic reverse-micelle system. The effects of various factors, such as the mixing ration (r) between the anionic and cationic surfactants, the temperature, and the presence of polymeric additives, o nthe formation of tha nanobelts and their hier-archical assmbly have been examined in detail. In particular, r has been shown to be powerful in modulating the formation and assembly of th BaMoO4 adn BaWO4 nanobelts. Architectural control fo the penniform nanobelts superstructures has been readily achieved by changing the experimental parameters. A plausible two-stage growth mechanism has been proppsed for th formation fo penniform BaXO4 nanobelt supersturctures i ncatanionic rverse micelles.