Abstract: Based on the principle of color reaction of Fe(Ⅱ) with o-phenanthroline, a reagent tablet used specifically for rapid field analysis of water samples for iron contents was prepared and tested. Powdered reagents of sulfamic acid, o-phenanthroline, hydroxylamine hydrochloride and sodium acetate with their mass ratio of 0.2 g∶0.003 g∶0.03 g∶0.3 g respectively were mixed thoroughly and pressed into a tablet having its diameter of 10 mm and thickness of 0.3-0.4 cm under a pressure of 5 MPa with a tabletting press. When in use, one piece of the tablet was added into 10 mL of water sample, measure the absorbance of the solution at 510 nm 5 min after complete dissolution of the tablet. Standard working curve with linearity range between 0.2 to 4.0 mg·L-1 was prepared by using Fe(Ⅲ) standard solution. Detection limit (3σ) found was 0.07 mg·L-1, and value of RSD (n=6) found was 0.57% at the concentration of 1.5 mg·L-1 of Fe(Ⅲ). Three kinds of water samples were analyzed by this method, giving values of Fe-contents in consistency with those obtained by the GB standard method.