To provide a soil treating material which exhibits more excellent capacity for adsorbing fluorine when applied to fluorine-contaminated soil and from which the once adsorbed fluorine is restrained from being eluted again.

The soil treating material for insolubilizing fluorine contains an iron oxide (1) having 100 m2/g specific surface area at the least and at least one aluminum compound (2) selected from aluminum hydroxide and a compound for producing aluminum hydroxide when hydrolyzed or neutralized. The soil decontaminating method comprises a step of adding the soil treating material to the fluorine-contaminated soil.