[en] The radiation chemistry reactions of Procion Brilliant Blue HGR and Methylene Blue in aqueous solution with γ-ray was studied; especially, the color fading yield G(-dye) in the coexistence of CO₃^2-, SO₄^2- or Br^- ions and the reaction mechanism. In the O₂-saturated system, the G(-dye) values of the former in low concentration at [CO₃^2-] = 0 and = 200 mM or above are 0.54 and 2.2, respectively. However, the latter Methylene Blue was not faded due to the oxidation by CO₃^-. In the SO₄^2- system, the G(-dye) values of both samples were not influenced. Then, in the N₂O-Br^- system, the former faded due to the oxidation by Br, (BrOH)^-, Br₂^- or Br₃^- ion radical; but the latter was not faded by Br₃^-. In the irradiation of the model dye waste waters of 13 different reactive dyestuffs containing Na₂CO₃ and Na₂SO₄, the estimated G(-dye) values varied largely between about 0.1 and 2.0, much influenced by the coexisting CO₃^2-. (J.P.N.)