Functionalities of organic semiconductors are governed not only by individual molecular properties but also by their weak intermolecular interactions in various conformations. The individual molecular property has been widely investigated in detail; on the other hand, the weak intermolecular interaction is difficult to investigate precisely due to the presence of the extrinsic energy broadening in organic solids such as structural disorders. Here we review the recent progress in the valence band dispersion of organic materials studied by using angle-resolved photoemission spectroscopy (ARPES). The novel ARPES technique reveals the precise band-dispersion measurement of sub-0.1-eV scale in molecular crystalline films, which enables us to discuss the quite weak but essential intermolecular interaction systematically based on the chemical substitution of constituent elements in the molecule. The precise and systematic band-dispersion measurement would be a credible approach towards the comprehensive understanding of the intermolecular interaction and the resultant charge transport property as well as their tuning by substituents in organic molecular systems.