PROBLEM TO BE SOLVED: To provide an efficacy enhancing agent composition for agrochemical in a solid form that uses a cellulose derivative that enhances the efficacy of an agrochemical, and is excellent in solubility to water, and an agrochemical composition using the same.SOLUTION: The solid efficacy enhancing agent composition for an agrochemical comprises (A) one or more cellulose derivatives selected from hydroxypropyl cellulose and hydroxypropyl methylcellulose, (B) one or more compounds selected from polyethylene glycol, glucose, fructose, and sucrose, and (C) one or more surfactants selected from alkyl sulfate having an alkyl group with a carbon number of 12 or more and 16 or less, and alkylbenzene sulfonate having an alkyl group with a carbon number of 12 or more and 16 or less.SELECTED DRAWING: None
