Luminescence behavior of Ru(bpy)(3)(2+) (bpy = 2,2＇-bipyridine) and Ru(bpy)(bpds)(2)(2-) (bpds = 2,2＇-bipyridine-4,4＇-disulfonate dianion) in aqueous solution of cobalt(III)-complex-containing poly(methacrylic acid) (Co(III)PMA), which is affected by a unique pH-induced conformational transition, was investigated by means of fluorescence spectroscopy. The bell-shaped pH dependence of the luminescence intensity of the photoexcited Ru(bpy)(3)(2+) with a maximum value at pH 5 was observed for Ru(bpy)(3)(2+) in Co(III)PMA solutions. The maximum wavelength of the luminescence (lambda(max)) also depended on pH and the blue shift was observed at pH 5. The luminescence behavior of the photoexcited Ru(bpy)(bpds)(2)(2-) was independent of pH in Co(III)PMA solutions. The Ru(bpy)(3)(2+) species were strongly interacted with CoPMA at pH 5, while the Ru(bpy)(bpds)(2)(2-) species had no interaction. Stern-Volmer plots for the quenching of Ru(bpy)(bpds)(2)(2-) with Co(III)PMA gave straight lines at various pH, The fact also indicated that the Ru(bpy)(bpds)(2)(2-) species have no interaction with Co(III)PMA at any pH. The observed quenching constants significantly depended on pH and sharply decreased in the pH range of 3.5 to 5, It was suggested that the quenching reaction was influenced by the pH-induced conformational transition of Co(III)PMA.