Fine crystals of sodium hexatitanate (Na2Ti6O13) were prepared by a flux method for photocatalytic steam reforming of methane (PSRM) to produce hydrogen. The examined parameters for the preparation in this study were the solute concentration in the molten sodium chloride salt and the cooling rate from the molten mixture. As a reference, another sample was prepared by a solid state reaction method, which corresponds to the preparation without the sodium chloride flux. The prepared samples consisted of hexagonal rod-like microcrystals of monoclinic structure with various morphology, particle size, crystallite size, aspect ratio, and specific surface area. The solute concentration affected the length and the aspect ratio of the rod-like structure although the cooling rate did not so much. The samples were loaded with 0.05 wt% of Rh cocatalyst nanoparticles, which was well dispersed oxide species on the surface. The Rh-loaded samples exhibited photocatalytic activity for hydrogen production in the PSRM. It was found that the photocatalytic production rate varied with the various structural parameters, especially correlated with the crystallite size of the rod-like Na2Ti6O13 fine crystals.