The redox peak current of the Ti(IV)/Ti(III) pair for titanate-nanotube (TNT) film-covered basal plane pyrolytic graphite disk electrode (PGE) was found sensitive to the varying concentration of nitrate in the acetate buffer solution. The TNT/PGE shows stable redox peak in 0.1M acetate buffer, which disappeared when changed into the same buffer solution containing over 5.6 mM nitrate. The return of the TNT/PGE into bare acetate buffer induced a full recovery of the redox peak of Ti(IV)/Ti(III). These effects can be repeated, just as a switch with on/off function. The electrochemical activity of titanium oxide on the electrode surface can be reversibly retrieved between 0.1M acetate buffer solution (pH 5.5) and nitrate. This system may be applicable to designing nitrate sensor.