It is well-known that primary amines form inclusive complexes with crown ethers. This kind of noncova-lently inclusive complexes,exemplified tryptophan complex with 18-crown-6,was studied by combination of two experimental methods,fluorimetry and mass spectrometry,with theoretical calculation. Fluorescence intensity of tryptophan in the absence and the presence of 18-crown-6 in aqueous HAc-NaAc buffer solution at pH=3.73 has been studied by fluorometry. The fluorescence intensity decreases significantly with increasing the concentration of 18-crown-6. The association constant K for the 1:1 complex of tryptophan ion-18-crown-6 was determined by means of fluorimetry. Mass spectrometric study of the complex gives direct evidence of the complex in the gas phase whose structure and binding energy are properly predicted by ab initio calculation. It is well-known that primary amines form inclusive complexes with crown ethers. This kind of noncova-lently inclusive complexes, try tryptophan complex with 18-crown-6, was studied by combination of two experimental methods, fluorimetry and mass spectrometry, with theoretical Fluorescence intensity of tryptophan in the absence and the presence of 18-crown-6 in aqueous HAc-NaAc buffer solution at pH = 3.73 has been studied by fluorometry. The fluorescence intensity decreased significantly with increasing concentration of 18-crown-6 . The association constant K for the 1: 1 complex of tryptophan ion-18-crown-6 was determined by means of fluorimetry. Mass spectrometric study of the complex gives direct evidence of the complex in the gas phase whose structure and binding energy are properly predicted by ab initio calculation.