Abstract: A series of different structural magnesium metallic complexes of meso-tetrakis (4-alkoxyphenyl) porphyrins was characterized by laser desorption ionization time-of-flight mass spectrometry (LDI-TOF-MS). The effect of different length alkane chain on the result of mass spectrometry for the metallic complexes was investigated and the reliable molecular weight was obtained. LDI-TOF-MS is very effective for analysing the novel metallic complexes of meso-tetrakis (4-alkoxyphenyl) porphyrins.