A Co(III) complex possessing selective nitric oxide (NO) capturing ability was immobilized onto a bulky phosphonium type ionic liquid-modified Au electrode, IL/Au, (Co@IL/Au), which was confirmed by several physicochemical methods, such as IR-RAS and electrochemical measurements. The Co@EL/Au exhibited a significant change in its chemical properties after reaction with NO, indicating that it captures the NO molecule. Furthermore, it might be able to determine the quantity of NO concentration in an aqueous solution only in a low concentration range of NO, from 0 to 160 ppb.