Disclosed is an agent for improving alkali resistance of a plant. Also disclosed is a method for improving alkali resistance of a plant, which is characterized by using the agent for improving alkali resistance of a plant. Specifically disclosed is an agent for improving alkali resistance of a plant, which is characterized by containing 5-aminolevulinic acid, a derivative thereof or a salt of any of them, and an iron compound. Also specifically disclosed is a method for improving alkali resistance of a plant, which is characterized by using such an agent for improving alkali resistance of a plant.