The present invention provides a pesticide composition comprising a pesticidal active ingredient and a compound represented by chemical formula (I) or chemical formula (II) R—O-(EO)w-(PO)x-(EO)y-(PO)z-H  (I) R—O—(PO)w-(EO)x-(PO)y-(EO)z-H  (II) (wherein, EO represents an ethyleneoxy group, PO represents a propyleneoxy group, R represents an alkyl or alkenyl group having 8 to 20 carbons, w represents on average an integer in the range of 1 to 25, x represents on average an integer in the range of 1 to 25, y represents on average an integer in the range of 1 to 25, and z represents on average an integer in the range of 1 to 25). Further the present invention provides a method for potentiating the efficacy of the pesticidal active ingredient comprising using a compound represented by chemical formula (I) or chemical formula (II) in combination with a pesticidal active ingredient.