Organic molecular beam epitaxy (OMBE) is the growth technique assuring high quality films and properly designed multilayers of organic molecular materials in view of both their fundamental studies and applications. To monitor in-situ the OMBE growth, we have applied reflectance anisotropy spectroscopy (RAS), which is particularly effective and sensitive, being non destructive for organic materials. In this work, RAS is used to monitor, in-situ, the growth of organic heterostructures. The experiment is carried out using organic single crystals as substrates and oligothiophenes as molecular materials to build a stack of layers. A layer-by-layer growth of the films is demonstrated, together with the formation of interfaces with peculiar optical behavior and structure. (C) 2008 Elsevier Ltd. All rights reserved.