Abstract: A new synthetic way of magnesium tetraphenyl porphyrin (MgTPP) was presented, by which MgTPP was synthesized with tetraphenyl porphyrin and magnesium acetate, and purified by chromatography. The purified sample was confirmed as MgTPP by UV-Vis spectral method, 1H-NMR method, and matrix assisted laser desorption ionization time of filight mass spectrometry (MALDI-TOF-MS) method. The sample’s Soret band was shown at 424 nm, and Q band was shown at 563 nm and 602 nm in UV-Vis spectra. In addition, the spectral characters of MgTPP were studied after irradiating with incandescent light by UV-Vis spectral method and fluorescence spectral method. The results showed that the Soret band of MgTPP decreased remarkably with the increasing of irradiation time in the UV-Vis spectra, and fluorescence quenching was observed in the fluorescence spectra with 550 nm as excitation wavelength. Meanwhile, a new molecular ion peak 668 (m/z) in the MALDI-TOF-MS was shown, indicating that the coordinated complex of MgTPP-O2 may be formed by the photochemical interaction between MgTPP molecules and oxygen molecules under the illumination condition.