Hemin (iron(III) protoporphyrin IX chloride) and mixed hemin/n-octadecylamine (ODA) with the molar ratio of 1:2 were used to investigate the Langmuir monolayer behavior and to prepare the Langmuir-Blodgett (LB) films. It showed that well-defined Langmuir monolayers were formed at the air-water interface and could be successfully transferred onto solid substrates. UV-vis spectra of hemin indicated the formation of H-aggregate in a LB matrix for the blue shift of the Soret band from 400 nm in solution to 370 nm in LB film. The inlay of ODA molecules partly reduced the aggregation of hemin molecules. Both the small-angle X-ray diffraction (XRD) pattern of hemin and mixed hemin/ODA LB multilayers exhibited an ordered layer structure in an LB matrix with the d-value of bilayer hemin equal to 4.8 nm. Surface photovoltage spectroscopy (SPS) was used to study the photoinduced interfacial charge-transfer process between a monolayer or multilayer of hemin and mixed hemin/ODA LB films on n- and p-type Si substrates. The results showed that the hemin LB monolayer film had a photosensitization effect on n-type Si. Particularly, the photovoltaic response value at the region of 400 nm which corresponds to the Soret band absorption of hemin molecules was increased 6-fold. The mixed hemin/ODA LB monolayer and multilayer films increased the photovoltaic conversion efficiency by separating the hemin molecules into individual ones with about a 15-fold and 7-fold increment of response value at the Soret band, respectively. But the SPS response value of the hemin LB multilayer film was decreased almost 20-fold and the photovoltaic conversion efficiency was largely reduced.