Using a thin film of metallic tin as catalyst, ultrasmall single-crystalline zinc oxide nanobelts have been synthesized in large quantity using a simple solid-vapor technique. The nanobelts have an average width of 5.5 nm and a narrow size distribution of +/-1.5 nm. The nanobelts grew along the [0001] direction, with (2110) top/bottom surfaces and (0110) side surfaces. Photoluminescence measurement showed a blue shift in the emission spectrum compared to that acquired from ZnO nanobelts of similar to200 nm in width. These ultrafine nanobelts should be good candidates for investigating size-induced electrical and optical properties of functional oxides.