For the purpose of,characterizing the water-soluble ferrous iron in paddy soils,the iron was determined as metal ions and those complexed by organic matter separately. A certain amount of a-a' dipyridyl solution was added to the water extract,and the color intensity was measured at different time intervals. Maximum color intensity was usually obtained after 48 hours. The amount of iron corresponding to the respective color intensity was plotted against the logarithm of rime in seconds,and the extrapolated intersection at zero time was taken as the metal ions. The amount of compleged iron was calculated as the difference between the amounts of total ferrous iron and that of metal ions.