Novel water-soluble azo compounds useful as raw materials for preparing dyes excellent in dyeing properties and fastness and prepared from a coupler consisting of 2-hydroxynaphthalene-3,6-dicarboxylic acid or an ester thereof or an amide derivative of the same and a diazonium compound having a group of the general formula: -B-(CH 2 ) 2 -Q or -B'-(CH 2 ) 2 -Q' (wherein B and B' are each an electron-attracting group; and Q and Q' are each a group capable of forming a vinyl group through the elimination with an alkali, provided the groups Q and Q' are each bonded at the β-position of the ethyl group).