A molecular photodiode was fabricated with the hetero-langmuir-Blodgett (LB) film consisting of an electron acceptor (A), a sensitizer (S) and an electron donor (D). N-Docosylquinolinium TCNQ, 10-(1-pyrene) decanoic acid and 1-1’-ferrocene-N-dioctadecyl carboxamide were used as A, S and D units, respectively. One-way electron transfer from D to S was observed with cyclic voltammetry for the modified electrode containing complex S/D LB layers, Also, one-way electron transfer from S to A was observed based on the fluorescence quenching in the complex S/A LB layers. By aligning a hetero-LB film of A/S/D three units on ITO glass with an aluminum thin film, 3. molecular photodiode with the structure of metal/insulator/metal (MIM) was constructed, Due to excitation by irradiation with a 340 nm monochromatic light source, the photo-induced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The direction of energy flow was in accordance with the energy level profile across the LR films. The photo-switching function was achieved and the rectifying characteristic was observed in the molecular device.