We present a new kind of organic complex system of electrical bistability, m-nitrobenzal malononitrile and diamine benzene (mNBMN-DAB), which can be employed as ultrahigh density data storage devices by scanning tunneling microscopy (STM). The mNBMN-DAB thin film was prepared on highly oriented pyrolitic graphite (HOPG) substrates using physical vacuum deposition method. A critical voltage pulse between the STM tip and the surface of the HOPG substrate can make marks on the thin films. The size of the marks is about 1.3 nm and the corresponding data storage density is larger than 10(13) bits/cm(2). A new mechanism of the charge transfer in the system for the data storage is suggested. These results show a great potential of this type of organic composite systems in the application of the ultrahigh density data storage.