We have developed an optical sensor for determining and quantifying naphazoline (NPZ) based on its inherent fluorescence property. We have placed a non-ionic-exchanger solid support (Amberlite XAD-7) in a flow cell in the light path of the excitation beam and the fluorescence signal for NPZ is continuously monitored at lambda(exc/nm)=294/306 nm. The response time for this sensor is acceptably fast, 80s, obtaining a detection limit of 2.6 ng mL(-1) with standard deviations of 2.0% at 125 ng mL(-1). This device has been satisfactorily applied to two commercial formulations and its selectivity has been demonstrated with an interference study. The advantages have been compared with the only published sensor for determining NPZ in pharmaceutical preparations and with other analytical methods in the literature.