This paper describes the synthesis of poly(1-aminonaphthalene) and its application as a chemosensor for detection of Fe3+ using the naked eye and a fluorimetric method. The conjugated polymer was synthesized by chemical oxidative polymerization using FeCl3 as a catalyst. The response of the polymer towards various metal ions was investigated using colorimetric detection, and ultraviolet-visible and fluorescence spectroscopies. The polymer displayed high selectivity and sensitivity towards Fe3+ compared with other metal ions. A significant colour change from purple to yellow was observed upon addition of Fe3+ by the naked eye. The polymer also showed a high selectivity and sensitivity 'turn-off' fluorescence response towards Fe3+ ions. A good linear response was obtained for Fe3+ concentrations in the range 10-50 mg L-1 with a detection limit of 1.04 mg L-1 . The proposed chemosensor was applied for determination of Fe3+ content in water samples and satisfactory results were obtained.