The invention relates to the field of organic chemistry and medicine, and more particularly to a method of producing synthetic biologically active derivatives of carbopentoxysulfanilic acid. The present method of producing a sodium salt of (2,6-dichlorophenyl)amide carbopentoxysulfanilic acid is characterized in that the reaction mass formed during the production of (2,6-dichlorophenyl)amide carbopentoxysulfanilic acid is agitated in a medium which is acidified with a solution of hydrochloric acid to pH 5-5.5, and the isolated precipitate may be washed with water acidified with a solution of hydrochloric acid to pH 5-5.5. This increases the yield of a sodium salt of (2,6-dichlorophenyl)amide carbopentoxysulfanilic acid to 70% (compared to a prior art yield of 32%) and also increases the purity of the target sodium salt.