The surface states of niobium oxide superfine particles (NOSPs) are investigated by analyzing the pressure dependence of the dispersion of complex dielectric constants. NSOPs were formed by a magnetron sputtering system. The average size was 260 +/- 25 Angstrom. The lattice constant is a = 3.45 Angstrom (bcc). NOSPs were a metastable materials which contained 50 at% oxygen. The density distributions of electric dipoles due to the surface state on the particles were obtained by approximating the data with theoretical curves. The reactivity of NSOPs was investigated on O-2, Ar and N-2. The surface reactivity of NOSPs strongly depended on the oxidation process of the niobium superfine particles. The influences of adsorption of argon were observed at the frequency regions 200 Hz < omega < 3 kHz and 400 kHz < omega, where the electric dipole density increased above 0.1 Torr of argon. In N-2 gas, the anomalies of density of electric dipoles were observed at higher regions of the frequency and the gas pressure; 600 Hz < omega and P-N2 > 4 Torr, respectively.