The design and operation of a methanol concentration sensor suitable for use with direct methanol fuel cells is described. The sensing principle is based on the measurement of concentration-dependent oxidation currents for the electro-oxidation of methanol in a polymer electrolyte membrane cell at a platinum-ruthenium electrode. The device construction and properties are described. The sensor was integrated with an automatic fuel feed system, and was operated for several tens of hours. The results demonstrate that the sensor is robust and sensitive enough to meet the demands of concentration sensing and control in direct methanol fuel cell systems.