Dye molecules were suggested as a sensitive element for an optical sensor of parameters determining the efficiency of a fuel cell with a proton-exchange membrane, in which a water-methanol mixture is used as a fuel. The sensitivity of representatives of three different types of dyes to the concentrations of protons and methanol was examined. The optical spectra of dyes in water-methanol mixtures simulating the internal medium of Nafion type membranes for fuel cells showed that picric acid and Malachite Green can be used as optical sensors. The dyes of different type (triphenylmethane derivatives, diazo compounds, phenol nitro derivatives) can give response mainly to proton concentration or to proton and methanol concentrations simultaneously.