Silica based adsorbent sequentially modified with polyhexamethylene guanidine and 7-iodine-8-hydroxyquinoline-5-sulfonic acid (Ferron) was proposed for adsorption-photometric and test-determination of Fe(III) in natural water. During adsorption of Fe(III) from solutions with pH 2-4 adsorbent became green colored. Formation of green-colored surface complex of Fe(III) with Ferron with the maximum in diffuse reflectance spectrum at 600 nm was used for developing the procedure of its adsorption-photometric determination. Detection limit calculated by 3s-criterion was 0.03 µg/0.1g of adsorbent (3 µg/L if the adsorption was carried out from 10 mL of solution); the analytical range was 10 – 220 µg/L. Test-method was proposed for quick visual determination of Fe(III) in natural water in the variant of test-scale. Developed procedures were tested for determination of iron in natural river water of Krasnoyarskii kray and mineral water “Zagorie”.