A synthesizing method of ramalin, their salt or solvate is provided to have excellent oxygen-resistant and anti-inflammatory activity. A synthesizing method of ramalin, their salt of solvate is in the chemical formula of the final step of the drawing, comprises: a step of reacting L-glutamic acid, in which carboxylic group of the first carbon and amino group of second carbon are protected, with 2-hydrazinylphenol; and a step of removing protection.