Spherical powders of NaTaO3-C composite were prepared by a step process in a continuous spray pyrolysis reactor and tested their photocatalytic activity in a continuous slurry reactor for the production of hydrogen from water. Effects of carbon contents in the composite on the crystal, surface property, shape, optical absorption response and efficiency of hydrogen production of the composite were examined. The crystal of NaTaO3-C composite was analyzed by XRD analysis. From the analysis of SEM images, the prepared composite powder was found to be spherical with rough surface. The roughness of the composite surface became noticeable with increasing carbon content in the composite. The concentrations of all elements in the composite were determined by energy dispersive spectra (EDS). From the analysis of optical response, which was analyzed by diffuse reflectance spectra (DRS), the absorption edge of NaTaO3-C composite was extended to the whole visible light range. The extension to the visible light absorption edge became drastic with increasing carbon content in the composite up to 8.98 wt.%. However, this shift is not directly related to the band change because there is no evidence that carbon is incorporated in the lattice of NaTaO3. (C) 2009 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.