To provide a method for producing high-purity 1,3,6- hexanetricarboxylic acid with a low hue and excellent thermal stability, obtained from 1,3,6-tricyanohexane by an electrolytic reducing reaction of acrylonitrile according to simple and industrial treating procedures.

This method for producing the 1,3,6-hexanetricarboxylic acid and/or its salt is carried out as follows. A trinitrile mixture consisting essentially of the 1,3,6-tricyanohexane is separated from an electrolyte consisting essentially or adiponitrile and obtained by the electrolytic reducing reaction of the acrylonitrile. The 1,3,6-tricyanohexane in the mixture is hydrolyzed and then crystallized.