Asimple spectrophotometric flow-injection method is reported for the highly sensitive and fast determination of iron(III) and total iron. The method is based on the formation of iron(III)- (1-nitroso-2-naphthol-3,6 sulphonate) (NRS) complex. The optimum conditions for the reaction of iron(III) with NRS is studied. And the complex is selectively monitored at λmax370 nm. With the reagent carrier solvent used was 5x10-4 M 1-nitroso2-naphthol-3,6 sulphonate in 0.1 M acetic acid-acetate buffer solution at pH 4.0. Parameters affect simultaneously for the determination of iron(III) and interfering ions were tested. Relative standard deviation for five consecutive injections of 70 µg.L-1 iron(III) was 1.46% and for 5 µg.L-1 iron(III), it was 3.12%. The calibration graph was linear in the iron(III) concentration range 0.1-100 µg.L-1 and the limit of detection was 0.05 µg.L-1 for a 20 µL injection volume. The precision and accuracy of the method were checked by analysis of certified reference material and AAS method. The method was successfully applied to determine trace amounts of iron(III) and total iron in river and sea water samples.