Wastewater treatment based on solar energy effected photocatalytic reaction is a green process that utilizes renewable energy resources and minimizes secondary pollution. Low conversion efficiency is one of the key issues to overcome for realizing its practical application. With an aim at significantly raising the process efficiency, a rotating disk reactor (RDR) has been evaluated for the application of photocatalytic decomposition of dye pollutants in water. In this process, photocatalyst (TiO2) particles are immobilized onto a disk (6 cm in diameter), and dye (methyl orange)-containing solution is allowed to flow in radial direction along the surface of the disk, which is rotating and illuminated with UV light. The correlations between the fundamental characteristics of the reactor, including residence time and film thickness, and its operating variables, including volumetric flow rate and disk rotating speed, have been established by the combination of fluid dynamic and kinetic models. The results indicate that the reactor can be operating beyond mass-transfer limitation by reducing the liquid film thickness, which is a complex function of both flow rate and disk rotating speed, below certain critical value. Even under such a condition, the overall reaction rate remains strongly affected by the liquid film thickness due to the intensity attenuation of incidence light through the liquid film before reaching the TiO2 surface. With selected operation conditions, conversions greater than 50% have been achieved within only a few seconds of residence time. A reactor design equation has been derived, indicating promising scale-up potential of the process.