The characteristics of host-guest complexes between cucurbit[n]uril (CB [n]) and phenylalanine were investigated by UV-visible absorption spectroscopy in acetate buffer solution at room temperature. It was found that the UV-visible absorption increased steadily with constantly dropping the high concentration of cucurbituril (CB ) and cucurbituril (CB ) in the phenylalanine solution which indicates that there are some interaction betweenCB [n] and phenylalanine.Then CB  and phenylalanine at molar ratio of 1:1 to weigh while CB  and phenylalanine at molar ratio of 1:2, respectively, are both demonstrated by 1H NMR spectra. 1H NMR spectrum of complexes was obtained, indicating an enthalpic driving force for host-guest complexes. The possible interaction mechanism and inclusion mode were also discussed. This work may extend the application range of CB [n] in supramolecular and pharmaceutical analysis.