Marmin is a coumarin derivative compounds isolated from the bark and roots of Aegle Marmelos Correa. Previously, ethanolic extract of leaves of Aegle Marmelos Correa on isolated ileum showed antagonism effect on the contraction induced by histamine. Besides H 1 receptor, there is also muscarinic acetylcholine (AChM)receptors involved in the mechanism of ileum contraction. Marmin is predicted to antagonize on AChM 3 receptors.This study aimed to determine the effect of marmin on smooth muscle contraction of isolated guinea pig ileum induced by metacholine, an agonist of AChM 3 receptor. The method in the study were in vitro (isolated organ) and in silico (docking PLANTS). In the in vitro study, marmin exhibited a competitive antagonists effect at the concentration of 100 μM (pA 2 value of 1,728) on the AChM 3 receptors. Reversibility assay on AChM 3 receptors showed that by washing the ileum with Tyrode buffer every 6 minutes for 30 minutes, the bond of marmin to the receptor was still not completely detached. In the in silico study, marmin was observed to be bound to AchM 3 receptors (docking score: -102.086). Marmin bond was weaker than that of native ligand of AChM 3 receptor (tiotropium, docking score: -115.107), however, stronger than that of AChM3 receptor agonist and antagonist. Based on the results, we conclude that marmin have a competitive antagonist activity on AChM 3 receptor.