In this paper, the formation, structure, and photophysical properties of functional mixed film of 5,10,15,20-tetra-4-(2-decanoic acid)phenyl porphyrin (TDPP) with TiO2 nanoparticles formed from the 2D sol-gel process of tetrabutoxyltitanium (TBT) at the air/water interface is reported. The composite multilayer films were assembled by transferring the mixed monolayer onto quartz plates. The diameter distribution and crystallinity of TiO2 particles were estimated by TEM observation and electron diffraction. The sensitization of TDPP upon TiO2 nanoparticles was confirmed by the spectral changes of UV-visible absorption and fluorescence of TDPP in the composite films. Furthermore the photosensitization greatly affected the photocatalytic activity of TiO2 particles with respect to the degradation of methylene blue (MO).