KOH-impregnated activated carbon (K-IAC) was studied as a NOx adsorbent. When adsorbing NO2/air to K-IAC, as the concentration increases, the removal efficiency relatively decreases because the function of the selective adsorption site for NOx is lost faster. By using AES/SAM and ToF-SIMS, we examined the chemical characteristics created on K-IAC through adsorption of NOx. Oxide crystals formed on the surface of K-IAC after adsorption of NO, was a result of the chemical bond among K, N, and O. KNO3 was predominantly distributed on the external surface, and the pore of K-IAC showed blocking from the crystal growth of KNO3. The results showed that surface basic OH-, well developed on the surface because of KOH impregnation, acts as a selective adsorption site. This study pointedly illustrates selective adsorption behavior from strong chemical interaction between NOx and K-IAC.