Plasmonic phenomena have greatly contributed to nanooptics and nanophotonics owing to their features such as light localization and high sensitivity to the surrounding environment. The nanoparticles of poor metals (e.g. Al) exhibit plasmonic properties in the UV range (240-350 nm) where many organic molecules and semiconductors absorb light, which was recently confirmed and utilized in enhanced Raman spectroscopy and UV photocatalysis. The present study demonstrates the efficient TiO2 photocatalysis with indium nanostructures resonant in the near-UV range. Indium (In) nanograins were densely distributed on a TiO2 thin film, where methylene blue (MB) was applied to test the photocatalytic activity. The photocatalytic reaction was initiated by irradiating the samples with UV light, and the time-dependent decay of the MB absorbance was observed. A reaction rate was found to increase by factors as high as 7 while the enhancement of photocatalysis shows particle size dependence. The increase and downward trend in the enhancement shows a good agreement with that in the field intensity simulated by the discrete dipole approximation (DDA). Simulation results also suggest that the largest enhancement of photocatalysis be obtained with In nanograins whose resonance is close to the bandgap of TiO2. It is expected that the light at the absorption edge wavelength confined at plasmonic nanostructures effectively for the photocatalytic reaction.