Disclosed is a stabilizer which has an excellent stabilizing action to a composition containing a water-soluble polymer thickener. This stabilizer enables to suppress turbidity, decrease in viscosity or change in pH of the resulting product due to deterioration of the thickener even when the product is stored for a long time. Specifically disclosed is a stabilizer for a composition containing a water-soluble polymer thickener, which contains a thiosulfate as an active ingredient. Also disclosed is a method for stabilizing a composition containing a water-soluble polymer thickener, which method is characterized by blending a thiosulfate in the composition.
