In this paper, iron in kaolin is divided into soluble and insoluble iron. The soluble iron in kaolin can be obtained by leaching with hydrochloric acid, while the total iron is achieved by calcining with sodium hydroxide. The relative standard deviation of this method is less than 5%, and sample recoveries range from 95% to 105%. The detection limit of iron is 1.06 μg/g. Other elements in kaolin did not interfere with iron determination by this method. Soluble iron was almost free iron with little structural iron in kaolin. The maximum content of removal iron for the whitening technique can be estimated by quantitative analysis of soluble iron in kaolin.