Photocatalytic BaTi4O9/RuO2 nanocomposites have been prepared by a solution-based impregnation method for overall water splitting into H-2 and O-2 under ultraviolet light irradiation. Although the specific surface area of BaTi4O9 nanobelts is far larger than that of the counterpart bulk, the nanobelts do not exhibit a much higher photocatalytic activity than the corresponding bulk. Our results suggest that the photocatalytic efficiency of nanocrystals can be significantly affected by the defects, which may further indicate the benefit from the size reduction can be canceled by a higher electron-hole recombination rate due to the defects. Furthermore, the absence of reactive facets in BaTi4O9 nanobelts may be another reason leading to the decrease of photocatalytic efficiency of nanocrystals. (C) 2012 Elsevier Ltd. All rights reserved.