In oxygen-free aquatic environments, such as groundwaters and hypolimnetic waters of eutrophic lakes, iron exists predominantly in the ferrous, Fe(II), state. In these waters certain natural organic compounds like humic materials also exist. The aim of this study was to find out the effects of tannic acid, acetic acid and glucose on converting/stabilizing Fe(II) to Fe(III). Experimental studies have been carried out in two-stage batch systems. In the first stage, the catalytic effect of Fe(III) on ferrous iron oxidation by atmospheric oxygen was studied at the concentration range of 0-1500 mg/l Fe(III), keeping Fe(II) constant at 25 mg/l. It has been found that kcat increases linearly with increasing Fe(III) concentration up to about 500 mg/l and this rate decreases beyond this value. In the second stage, a study has been made of how oxidation of Fe(II) and the catalytic effect of Fe(III) are affected by tannic acid, acetic acid and glucose. The results of this stage are that tannic acid completely inhibited the oxidation of ferrous iron, but acetic acid and glucose had no observable effect on the oxidation reaction.