Nanometer scale data recording has been achieved on p-nitrobenzonitrile thin films using scanning tunneling microscopy.When a series of voltage pulse is applied between the STM tip and the highly ordered pyrolytic graphite substrate, structural transition at molecular scale has been observed directly for PNBN thin films.The recording mechanism is attributed to local structural transition at molecular scale,i.e.,from a crystalline state to a disordered one.The former corresponds to a high electrical resistance,and the latter to a low resistance.