Mixed-potential type ammonia sensors based on yttria-stabilized zirconia are promising devices in NO x reducing system for high-temperature exhaust. However, selectivity is a critical issue that should be urgently addressed. Herein, a novel bilayer Cr 2 O 3 |In 2 O 3 sensing electrode (SE) was designed to improve the selectivity of the ammonia sensor, in which an additional Cr 2 O 3 layer was deposited on In 2 O 3 SE. The selectivity was examined in NH 3 , CO, NO and NO 2 . Finally, the sensor with the bilayer Cr 2 O 3 |In 2 O 3 SE exhibits an improvement of NH 3 selectivity at 600 °C, which is attributed to the Cr 2 O 3 layer catalysing the removal of CO and NO x before the gases reach the triple-phase boundaries (TPBs). Furthermore, the mixed-potential model of the NH 3 sensor with the bilayer SE was identified using the polarization curves obtained in different concentrations of NH 3 . Additionally, the proposed sensor displayed a good repeatability and resistances to CO 2 and H 2 O. This innovative bilayer Cr 2 O 3 |In 2 O 3 SE is expected to be applied in high-temperature NH 3 detection.