An amperometric- type of hydrocarbon sensor using a single electrolyte plate of Ni-doped LaGaO3 based oxide was investigated for monitoring exhaust gas from an internal combustion engines. Compared to a simple mixed potential-type sensor, amperometric sensor using oxygen pumping current showed a wider range for hydrocarbon detection. In particular, current at 1 V application was mainly affected by hydrocarbon but not oxygen when Pt and La0.6Sr0.4CoO3 were used as active and inactive electrode for oxidation of hydrocarbon, respectively. Because the current linearly increased with increasing hydrocarbon, it was expected that the concentration of hydrocarbon in exhaust gas can be monitored with the current through the sensor element. The current of the developed sensor was hardly influenced by coexisting CO and H2O and was only slight influenced by O-2. Therefore, selective detection of hydrocarbon was expected. In addition, the sensitivity to hydrocarbon increased with increasing carbon number in the hydrocarbon and the sensitivity to CH4 was negligibly small. Consequently, the developed amperometric hydrocarbon sensor could detect hydrocarbon excepting CH4 with high selectivity. This is a suitable property for a sensor using for monitoring hydrocarbon content in the exhaust gas from internal combustion engines. (C) 2003 The Electrochemical Society.