PURPOSE: To obtain a dispersing agent for biocidal granule, composed of a copolymer of a sulfone group-containing monomer. hydrophobic monomer and hydrophilic monomer at a specific molar ratio and excellent in disintegrating and extending properties in water and also in disintegration ratio, i.e., granule hardness.

CONSTITUTION: A dispersion agent for biocidal granule composed of a copolymer containing 5-98mol% sulfone group-containing monomer [e.g. styrenesulfonic acid (salt)], 1-50mol% hydrophobic monomer (e.g. an alkyl unsaturated monocarboxylate or chain or cyclic olefin) and 1-80mol% hydrophilic monomer (e.g. an unsaturated monocarboxylic acid or unsaturated dicarboxylic acid) as essential constituent units. The above-mentioned dispersing agent is used as dispersing agent for biocidal granule compositions containing a biocide, such as insecticide, germicide acaricide or herbicide, and inorganic mineral fine powder as constituent ingredients. The dispersing agent has sufficient disintegrating and extending properties in water.