The objective of the invention is to provide a plant activator with superior resistance-inducing activity and growth promoting activity and low toxicity and soil contamination. A plant activator comprising a fatty acid metabolite obtainable by a metabolism of a fatty acid with 4 to 30 carbon atoms by a proteobacteria under a dissolved oxygen concentration of 0.1-8 mg/L, and a method for manufacturing a plant activator comprising a fatty acid metabolite, comprising a step for fatty acid metabolism wherein a fatty acid with 4 to 30 carbon atoms is subjected to a proteobacterial metabolization under a dissolved oxygen concentration of 0.1-8 mg/L. A method for manufacturing a plant activator comprising a fatty acid metabolite, comprising a step for fatty acid metabolism wherein a fatty acid with 4 to 30 carbon atoms is subjected to a proteobacterial metabolization under a dissolved oxygen concentration of 0.1-8 mg/L.
