It is white crystalline powder. Odorless, slightly bitter, slightly soluble in water (1.14%, 25℃), insoluble in ethanol. Soluble in dilute acid or alkali. mp289℃(decomposition). Coloration by prolonged light exposure. A small amount of indole is produced by co-heating with water, and a large amount of indole is produced by heating in the presence of sodium hydroxide and copper sulfate. It is more stable when heated with acid in the dark, but it is highly decomposed when heated with other amino acids, sugars and aldehydes. When protein is decomposed with acid, tryptophan is completely decomposed.