Abstract: Provided are a rheology modifier and a method for modifying water rheology for imparting thixotropy and viscosity to water, and a slurry composition having high viscosity and excellent resistance to separation in water and a method for producing such a slurry composition. A rheology modifier containing: (A) a sulfate or a salt thereof having a hydrocarbon group with 12 or more and 22 or less carbon atoms and an average number of moles of added alkylene oxide of 0 or more and 25 or less; and (B) a fatty acid alkanolamide having a fatty acid moiety with 10 or more and 22 or less carbon atoms.