Polystyrene (PS) opal and titania (TiO₂) inverse opal films were fabricated by the self-assembly colloidal crystal template technique. Based on Bragg’s law, these sensors were used to detect the different concentrations of ethanol solution. The results indicated that TiO₂ inverse opal films were advantageous over PS opal film for detecting the ethanol concentration. TiO₂ inverse opal films sintered at 600 °C retained the highest sensitivity for ethanol concentration identification, since the anatase phase was transformed into the rutile phase, which resulted in an enhancement of the refractive index, i.e., an increase in the amount of the red shift.