Photo-induced electron transfer in flavin-porphyrin hetero-type Langmuir-Blodgett (LB) films and its temperature dependence were investigated by means of the photocurrent measurements and the transient fluorometry. From 10 K to room temperature, transient photocurrent in sub-nanosecond time region was found to be independent of the temperature for a metal-insulator-metal device composed of the hetero-type LB films with a flavin-porphyrin molecular heterojunction (MHJ). This transient photocurrent was attributed to the charge separation (CS) process from the photo-excited flavin to the porphyryin at the MHJ on the basis of the temperature dependence of the fluorescence decay profiles of the excited flavin. By integrating these results with UV-visible absorption spectra, it was deduced that the fast temperature-independent CS process at the flavin-porphyrin MHJ was mainly due to the quantum electron tunneling regulated by high-frequency quantum modes of intramolecular vibrations. (C) 2004 Elsevier B.V. All rights reserved.