X-ray reflective measurements (XRR), atomic force microscopy and single wavelength ellipsometry were used to investigate the optical properties of thin L-leucine films deposited onto silicon substrates. The ellipsometry data (Psi,Delta) were fitted with a four-layer-model, and the optical refractive index of the L-leucine film measured with ellipsometry was determined to be 1.37. With the conventional effective medium approximation theory and the ellipsometry results, the density of the L-leucine nanofilm was determined to be 70% (0.81 g/cm(3)) of crystalline L-leucine. This value was in good agreement with the density of 69% (0.80 g/cm(3)) obtained with XRR measurement. The ellipsometry measurements also enabled us to estimate the surface roughness or absorption layer of the film. This procedure of combined XRR and ellipsometry measurements could be a powerful tool for the determination of the (otherwise hard-to-determine) refractive index in thin organic material films with a rough surface layer. (C) 2010 Elsevier B.V. All rights reserved.