The supramolecular interaction between N,N-diethyl-2-(1-naphthalenyloxy)propanamide (napropamide) and -cyclodextrin (-CD) has been studied by spectrofluorimetry. The results showed that -CD reacted with napropamide to form an inclusion complex with an association constant of 3.18×103mol−1. The composition of the complex was 1:1 (-CD: napropamide). Based on the significant enhancement of fluorescence intensity of napropamide in inclusion complex, a spetrofluorimetric method with high sensitivity and selectivity was developed for the determination of napropamide in aqueous solution. Under the optimum conditions, the complex had excitation and emission maxima at 285 and 339nm, respectively. The linear range of the method was 3.7-1500ngml−1 with a detection limit of 1.1ng ml−1. The proposed method was successfully used to determine napropamide in river water.