A slurry rheology modifier comprises a first water-soluble low-molecular compound [referred to hereinafter as compound (A)] and a second water-soluble low-molecular compound [referred to hereinafter as compound (B)] being different from the compound (A), wherein the viscosity of an aqueous solution at 20.degree. C. prepared by mixing an aqueous solution S.sub.A (with a viscosity at 20.degree. C. of 100 mPas or less) of compound (A) with an aqueous solution S.sub.B (with a viscosity at 20.degree. C. of 100 mPas or less) of compound (B) in the ratio of 50/50 by weight can be at least twice as high as the viscosity of either aqueous solution before mixed.