The present invention provides a plant-activating agent for improving the activity of plants efficiently without a chemical injury onto the plant. The plant-activating agent is selected from the group consisting of (1) an organic acid derivative which is derived from the organic acid having two functional groups and wherein at least one of the above-mentioned functional groups is bonded to a group containing 1 to 30 carbon atoms; (2) a compound represented by the formula (II): RCOO(AO)nX1   (II) wherein R represents an alkyl or alkenyl group having 11 to 29 carbon atoms; X1 represents a hydrogen atom, an alkyl or acyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or a counter ion; AO represents at least one group selected from oxyethylene, oxyprolylene and oxybutylene groups and may be random or block; and n represents an average number of moles added and is zero to 30; and (3) a glycerol derivative. If necessary, the agent is used together with a surfactant, a fertilizer component or a chelating agent.