Adsorption and desorption states of nitrogen monoxide (NO) on a Rh(1 0 0) surface have been studied by electron-stimulated desorption (ESD), Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD). After NO adsorption, three states of oxygen were distinguished by ESD. Two states of atomic oxygen formed by the dissociation of adsorbed NO are; an adatom state and an oxide state. The other state is NO molecule adsorbed on Rh(1 0 0). The adsorbed species identified by ESD and AES, and the desorbed species by TPD suggest that N-2 desorbed at around 300 K is formed by the reaction of an adatom nitrogen with an adsorbed NO on a Rh(1 0 0) surface and that N-2 desorbed at around 560 K is formed by the reaction of two adatom species of nitrogen.