Objective: The study was aimed to investigate the inhibitory effect of ethanolic extract of Curanga fel-terrae leaves (EECFL) against acetylcholine (ACh)-induced contraction of the ACh-muscarinic-3 receptor. Materials and Methods:The study of the inhibitory effect of the ethanolic extract on the contraction by ACh concentration series (10 −8 -10 −3 M) was conducted in vitro using isolated guinea pig tracheal organ in the Krebs solution.Results: Early incubation of tracheal organ with EECFL (0.5, 1, 2 and 4 mg/ml) before contracted by the series of ACh concentration produces the decrease of ACh contraction. The concentration series of ACh sigmoid curve rightward shift without decreasing the maximal contraction. The results of double-reciprocal plot of ACh shows the mean value of the 1/y-intercept of each extract was not different with the control. Conclusion:The EECFL showed competitive antagonist effect on ACh-muscarinic-3 receptors.