We report aggregated nanostructure formation of water insoluble meso-tetramesitylporphyrin (MTMP) induced by hydrogen chloride (HCl) vapor on a glass plate. The formation of aggregated nanostructures of MTMP was confirmed by UV-vis, time-resolved emission spectral techniques, atomic force microscopy (AFM), and high resolution transmission electron microscopy (HR-TEM). Exposure of HCl vapor to a thin film of MTMP, coated on a glass plate resulted in a 35 nm red shift of the Soret band in contrast to the case of MTMP thin film. AFM images showed the formation of MTMP aggregates induced by HCl vapor with the size of 50-170 nm in height and an average width of 120 nm. Protonation of MTMP coated on the glass plate by HCl molecules triggered the formation of aggregated nanostructures on the glass plate. Interestingly, it was found that the aggregates were not reverted back to the original morphology of MTMP thin film when it was deprotonated by exposure to ammonia vapor. The fluorescent lifetime of the MTMP thin film was decreased from 11.48 to 0.78 ns when it was exposed to HCl vapor, indicating the formation of MTMP aggregates on the glass surface.