To efficiently remove strontium from strontium-containing wastewater.

A method for treating strontium-containing wastewater includes adding, into the strontium-containing wastewater, a powder adsorbent such as zeolite, a laminar silica compound or titanate alkali metal salt that releases alkali metal ions to adsorb strontium in the strontium-containing wastewater, wherein the powder adsorbent is added as slurry of pH 9-14 with a solution with alkali metal ions dissolved therein as a dispersion medium. The adsorbent can thereby be held as the alkali metal ion type, and the adsorption capacity of strontium can be maintained high.