An effective method for producing a 1,2-naphthoquinone-2-diazide or a sulfo-substituted compound thereof from a 2-diazo-1-naphthalenesulfonic acid or a sulfo-substituted compound thereof. A 1,2-naphthoquinone-2-diazide derivative or a sulfo-substituted compound thereof is derived from a 2-diazo-1-naphthalenesulfonic acid or a sulfo-substituted compound thereof by use of an aqueous alkaline solution containing iodine; an aqueous alkaline solution containing iodine which is dissolved in an organic solvent; or an aqueous alkaline solution containing an oxidizing agent and iodine or an iodine compound.
