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

CONSTITUTION: 2,3,6-Trichloronaphthazarin and sodium methylate are heated under reflux in the presence of methanol to react these compounds and the resultant reaction product is subjected to solvent extraction and chromatographic treatment to provide the objective 2,3,6-trimethoxynaphthazarin. The chromatographic treatment is carried out in either of absorption chromatography, gel filtration chromatography and ion exchange chromatography. 2,3,6-trichloronaphthazarin which is a etarting raw material is obtained by heating and condensing 2,3-dichloromaleic anhydride with 2- chloro-1,4-hydroquinone in the presence of anhydrous aluminum chloride and sodium chloride at 160-250°C, preferably 200-220°C.