Hereunder presented is an AC impedance spectroscopic study of the lithium-inserted material LixLa1/3NbO3. Two semicircles were noted in accordance with the plots given as the complex impedance in the frequency region of 0.5 to 5000 Hz at room temperature, and these two semicircles made variation accompanied with the composition x. The dependence of the impedance spectra on the lithium salt concentration and temperature was examined, and it is explained that these two semicircles were in relation to the Butler-Volmer type kinetics. The evolution of impedance spectra for various conditions reveals that the electrochemical insertion process is described in terms of an adatom model; the resistance observed at a higher frequency region includes the adsorption and desolvation process accompanied with electron-transfer reaction. Furthermore, assignment as lattice incorporation, or insertion process at the electrode surface, is made with the other one observed in the lower frequency region.