An expeditious evaluation for photocatalyst is set up (or established) in this study. The optical transmittance of the methyl blue solution is measured, and a relationship between the transmittance of solution and its concentration is established. The performance of a photocatalyst can be evaluated via the distinct change of methyl blue solution. The TiO2 films performed as a photocatalyst were prepared using sol-gel method and then annealed by rapid thermal annealing (RTA). The samples were illuminated with a high-pressure mercury lamp for exciting photocatalytic reaction. The result shows that TiO2 photocatalyst degraded the methyl blue solution up to 97.8%.