The oxidative degradation rate, k(deg), of the solar cell dye (Bu4N+)(2)[Ru(dcbpyH)(2)(NCS)(2)](2-), referred to as N719 or [RuL2(NCS)(2)], was obtained by applying a simple model system. Colloidal solutions of N719-dyed TiO2 particles in acetonitrile were irradiated with 532-nm monochromatic light, and the sum of the quantum yields for the oxidative degradation products [RuL2(CN)(2)], [RuL2(NCS)(CN)(2)], and [RuL2(NCS)(ACN)], Phi(deg) was obtained at eight different light intensities in the range of 0.1-16.30 mW/cm(2) by LC-UV-MS. The Phi(deg) values decreased from 3.3 x 10(-3) to 2.0 x 10(-4) in the applied intensity range. By using the relation k(deg) = Phi(deg)k(back) and back electron-transfer reaction rates, k(back), obtained with photoinduced absorption spectroscopy, it was possible to calculate an average value for the oxidative degradation rate of N719 dye attached to TiO2 particles, k(deg) = 4.0 x 10(-2) s(-1). The stability of N719 dye during solar cell operation was discussed based on this number, and on values of the electron-transfer rate between [(RuL2)-L-(III)(NCS)(2)] and iodide ion that are available in the literature.