A fiber-optic sensor for copper based on reflection has been developed. It is prepared by immobilizing Nitroso-R salt on the DEAE Sephadex, the change of the reflected intensity at 520nm is proportional to the concentration of copper. The characteristics of the sensor have been studied by using the equilibrium and kinetics method. Because DEAE Sephadex is a colourless and transparent gel containing diethylamine glucan with low mass transfer resistance in water, the sensor reachs 90% of steady-static in 5 seconds; the sensor has no optical influence owing to no absorption at all in the visible region; the complex decomposes in 0.1 mol.dm^-^3 HCl, so the sensor has good sensitivity as well as good reversibility and has been successfully applied to the determination of copper ion in natural water and waste water.

Key words: COPPER ION, SENSORS, OPTICAL FIBER DEVICES, EQUILIBRIUM METHOD