Abstract. The local structure of Pd metal fine particles on LaFeO₃ which has a high catalytic activity was observed by dispersive XAFS optics from the viewpoint of dynamical structure change of Pd during oxide-metal change and CO/NO catalytic reaction. The oxide-metal change of Pd nanoparticles on LaFeO₃ and Al₂O₃ was investigated by 20–50 Hz rate. It was recognized that, under the reductive atmosphere, Pd atoms show similar speed of movement from oxide to metal state both on the two supports. However, under the oxidative atmosphere, Pd atoms on LaFeO₃ show faster movement from metal to oxide state than those on Al₂O₃. CO/NO catalytic reaction on Pd metal nanoparticles was also observed by 0.2 Hz rate. Slow observation mode made the four EXAFS parameters: coordination number, interatomic distance, Debye-Waller factor and edge shift, precisely determined during catalytic reaction. There are two particular differences between Pd particles on LaFeO₃ and Al₂O₃. Large enhancement of interatomic distance of Pd particle was only observed on Al₂O₃. Stable surface oxide layer of Pd particle is created on LaFeO₃.