We examined the inhibitory activities against monoamine oxidase (MAO) of Prunella vulgaris in vitro and in vivo methods. Methanolic extract of P. vulgaris showed significantly Inhibitorγ activities on MAO-A and MAO-B that were prepared from rat brain and liver in vitro. The inhibitory activities were measured by serotonin and benzylamine as substrates, respectively. MAO-A and MAO-B activities were potently inhibited by ethylacetate extracts of P. vulgaris in vitro tests. It was observed that those activities in vivo tests have different tendency each other. MAO-A activity was increased by the oral administration of methanolic extract of P. vulgaris while MAO-B activity was decreased. Consequently, we suggest that P. vulgaris may have the effects on the inhibitory activities against MAO both in vitro and in vivo.