At present, lean-burn type engines or diesel engines for passenger cars have been developed and installed into automobiles to improve fuel efficiency. In these cases, NOx storage catalysts or selective catalytic reduction (SCR) systems are also installed for reducing NOx emission. In order to control these systems more efficiently, NOx sensor which responds selectively, quickly, and quantitatively are necessary. Here we focused on the NO direct decomposition function of La-based perovskite oxides. We applied them to a sensing electrode for the amperometric NOx sensor using yttria-stabilized zirconia (YSZ). La_0.8Sr_0.2MO₃ (M = Co, Mn, Fe, Ni) powders were synthesized by means of spray pyrolysis method. Among four kinds of oxides studied, the sensor using La_0.8Sr_0.2MnO₃-SE showed the highest sensitivity to NO₂ as well as low base current even in the presence of excess O₂ (21 vol%). The sensor also exhibited excellent NO₂ selectivity at 500°C. The sensitivity was increased with an increase of NO₂ concentration in an examined range between 50 to 800 ppm, and did not change in the examined O₂ concentration range (5-21 vol%).