A Pd catalyst supported on Ba-substituted LaAlO₃ perovskite (Pd/La_0.9Ba_0.1AlO_3−δ) was investigated for NO reduction at low temperature by propylene, which revealed that Pd/La_0.9Ba_0.1AlO_3−δ has remarkably higher activity than other Pd catalysts at low temperatures (≤573 K) for NO reduction by propylene. To elucidate the surface reaction pathway, transient response tests were conducted using ¹⁸O₂. Also, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were conducted. Comparison with a Ba-impregnated catalyst (Pd/Ba/LaAlO₃) demonstrated that Pd/La_0.9Ba_0.1AlO_3−δ shows higher activity for the formation of oxygenated species (C_xH_yO_z) as an intermediate for NO reduction because the surface lattice oxygen has improved mobility via Ba²⁺ substitution in LaAlO₃. Therefore, Pd/La_0.9Ba_0.1AlO_3−δ have high activity for NO reduction, even at low temperatures in a humid condition.