The formation of thin films of a new C-60 derivative, C-60-NaDDC (C-60-sodium diethyldithiocarbamate), have been investigated at the air-water interface by using different surface methods. Thus, the surface pressure-surface area isotherm and the reflection spectra of the film at the air-water interface were measured and valuable information about the organization of the fullerene balls was achieved. The presence of the film and its state has been directly visualized at that interface by using Brewster angle microscopy (BAM). In addition, the ellipsometric angles, Delta and Psi, were measured by nulling ellipsometric measurements at the air-water interface allowing us to obtain the thickness of the C-60-NaDDC film. This value obtained from the combination of the reflection and nulling ellipsometry measurements is in a very good agreement with that expected from molecular models. (C) 2003 Elsevier B.V. All rights reserved.