The photocatalytic efficiency was improved with plasmonic nanoparticles resonant at the near-UV region. By applying indium (In) grains with the controlled size and density on TiO2, the production yield was improved to 6.4 times, while the reaction rate increased by 23.5 times. Structural observation and discrete dipole approximation simulation suggest that the photocatalytic efficiencies are derived from strong localized surface plasmon resonance at the absorption edge of TiO2 and a number of activated area.