The effect of concentration on scission of poly(vinylpyrrolidone) (pv = 6,700) in aqueous solution by high-speed stirring at a speed of 30,000 rpm at 30°C was investigated. Concentration was varied from 0.04 to 2% g/ml. Polymer chains were ruptured to lower molecular weights with decreasing concentration. The rate constant of scission, k, and the limiting degree of polymerization, Pl, in Ovenall's equation calculated for the results were considerably changed in the polymer concentration range from 0.2 to 1% g/ml. The effect of addition of methyl orange on polymer scission was then studied, because the dye had been reported to increase the viscosity of aqueous poly(vinylpyrrolidone) solution because of unfolding of the macromolecule chains. However, no significant effect was found in the concentration range from 0.034 to 0.34 in the molar ratio of methyl orange to poly(vinylpyrrolidone).