Monoamine oxidase is flavoenzymes, widely distributed in mammals. It is well recognized that MAOs serve an important role in metabolism that they have close relationship with health .Along with the discoveries between MAOs and neurotic disease, more and more studies have been jumped in .In this paper, we design a new probe for assaying the activities of MAOs. The results showed that the probe [7-(3-aminopropoxy)coumarin] is simple, effective and sensitive for MAOB.