3-Indoleacetic acid (IAA) is a kind of endogenous auxin ubiquitous in plants, belonging to indole compounds. It is an organic substance. Pure product is colorless leaf crystal or crystalline powder. Turns to rose color when exposed to light. It is easily soluble in absolute ethanol, ethyl acetate, dichloroethane, and soluble in ether and acetone. Insoluble in benzene, toluene, gasoline and chloroform. 3-Indoleacetic acid has a duality to plant growth, and different parts of the plant have different sensitivity to it.