Ultrahigh density data storage on a novel organic thin film by scanning tunneling microscope (STM) under ambient conditions is demonstrated. The material, N-(3-nitrobenzylidene)p-phenylenediamine (NBPDA), is used for preparing thin film by vacuum evaporation method. Crystalline NBPDA films with electrical bistability are obtained by this method. Recording experiment on the films is made by applying voltage pulses between the STM tip and substrate. The recorded marks are 0.7 nm in size, corresponding to a storage density of1014 bit/cm2.Current–voltage characteristic measurement shows that the resistance of the unrecorded region of the NBPDA films is much higher than that of the recorded region. The mechanism of recording is discussed. ©1998 American Institute of Physics.