Abstract: The mass spectrometric behavior of six 2-(4-arylphenyl)imidazo4,5-f-1,10phenanthroline compounds were investigated by the electrospray inonization multiple stage mass spectrometry. The fragmentation pathway of the compounds were depended on the group of 4-arylphenyl. When the 4-substituent group was an activating one, the fragmentation usually took place in the phenyl. While the 4-substituent group was deactivating, the fragmentation took place in the imidazole ring.