PURPOSE: To provide a method for producing 2,3,6-trichloronaphthazarin which is an active ingredient for antitumor agents.

CONSTITUTION: 2,3-Dichloromaleic anhydride is condensed with 2-chloro-1-4- hydroquinone under heating in the presence of anhydrous aluminum chloride and sodium chloride at 160-250°C, preferably 200-220°C to provide 2,3,6- trichloronaphthazarin. After terminating the condensation reaction, the reaction liquid is acidified and extracted with an organic solvent and further, the extracted liquid is subjected to various kinds of chromatographic treatments to purify the extracted liquid. Anhydrous aluminum chloride and sodium chloride used in the condensation reaction are generally used in a weight ratio of the former/the latter of 5:1.