A fractal memory function in the nanoscale biomolecular electronic device was investigated. Four functional molecules, cytochrome c, viologen, flavin, and ferrocene, were used as the electron acceptor, the relay, the sensitizer, and the electron donor, respectively. The hetero- Langmuir- Blodgett (LB) films were fabricated by sequential deposition of ferrocene, flavin, and viologen onto substrate. The cytochrome c-adsorbed hetero-films were prepared by the adsorption of cytochrome c onto hetero-LB films due to the electrostatic force. As the biomolecular photodiode, a metal/insulator/metal (MIM) structured electronic device was fabricated by the deposition of the aluminum onto the hetero-film. The transient photocurrent of the biomolecular photodiode was measured and the decay time constant was calculated as -0.146. The experiment and simulation of the response to the pulse train inputs corresponding to different ASCII codes were performed with the decay time constant, and the fractal memory effect of biomolecular photodiode was verified.