The structure and electronic state of fine Pt particles on the carbon electrode were investigated by XANES and extended x-ray absorption fine structure (EXAFS) spectroscopies. The white line intensities were processed into the parameter representing the density of unoccupied 5d state. They were described as kinds of voltammograms. It was different between the cathodic sweep and the anodic sweep even in the same potential. The small particle electrode showed large hysteresis of the d-density change. These changes by potential sweep are discussed in relation to the structure of the particle on the basis of the parameters of EXAFS. The large change in the small particle was explained by the ratio of the surface atoms in the whole particle. The thickness of the oxide layer and lattice disorder in subsurface was estimated from these structural parameters.