The Langmuir and Langmuir-Blodgett films of a benzo-18-crown-6-methanofullerene (1) were studied by spectrophotometry and Brewster angle microscopy. The surface pressure-area isotherm of the C-60 derivative (1) was obtained, and the compressibility of the isotherms was calculated. The addition of KCl to the water subphase stabilized the monolayer and increased the limiting area per molecule from 84 to 101 Angstrom, which is near the theoretical value. The changes of the Langmuir monolayer UV-vis spectra as a function of time are considered to be due to fullerene aggregation. Polymerization was not detected upon UV irradiation, in contrast to what has been reported in the literature. Brewster angle microscopy shows different aggregation proper-ties of the benzo-18-crown-6-methanofullerene (1) Langmuir monolayers on pure water compared to those on a 1 M KCl subphase.