Separation of active component derived from the methanol extract of Ruta chalepensis leaves was performed base on anti-asthma activities. Quinoline was isolated from the extract of R. chalepensis leaves through bioassay-guided fractionation. Quinoline had a strong relaxant effect ($IC_{50}$=0.42 mM) on the contractile activity of the isolated guinea pig trachea, and this relaxant effect was compared to that of five commercially available compounds. The structure-activity relationship revealed that quinoxaline ($IC_{50}$=0.46 mM) and quinazoline ($IC_{50}$=0.48 mM) have strong relaxant effects. The results indicated that R. chalepensis extract and quinoline derivatives have anti-asthma activity.