Renealmia alpinia (Zingiberaceae), a medicinal plant of tropical rainforests, is used to treat snakebites and other injuries and also as a febrifuge, analgesic, antiemetic, antiulcer, and anticonvulsant. The dichloromethane extract of R. alpinia leaves showed potent inhibition of human monoamine oxidases‐ (MAOs‐) A and B. Phytochemical studies yielded six known compounds, including pinostrobin 1, 4′‐methyl ether sakuranetin 2, sakuranetin 3, pinostrobin chalcone 4, yashabushidiol A 5, and desmethoxyyangonin 6. Compound 6 displayed about 30‐fold higher affinity for MAO‐B than MAO‐A, with Ki values of 31 and 922 nM, respectively. Kinetic analysis of inhibition and equilibrium‐dialysis dissociation assay of the enzyme‐inhibitor complex showed reversible binding of desmethoxyyangonin 6 with MAO‐A and MAO‐B. The binding interactions of compound 6 in the active site of the MAO‐A and MAO‐B isoenzymes, investigated through molecular modeling algorithms, confirmed preferential binding of desmethoxyyangonin 6 with MAO‐B compared to MAO‐A. Selective reversible inhibitors of MAO‐B, like desmethoxyyangonin 6, may have important therapeutic significance for the treatment of neurodegenerative disorders, such as Parkinson’s disease and Alzheimer’s disease.