The interfacial properties of the spread Langmuir films of C60Br24 and stearic acid have been studied at air-water interface by measuring their surface pressure-area isotherms. Monolayer studies on C60Br24 suggest a strong aggregation at air-water interface which corroborated the ab initio electron density calculations. The mixed films were found to be immiscible and non-ideal with an exception of X-C60Br24 = 0.5 which is the composition of greater stability. The interaction between C60Br24 and stearic acid results in the lowering of surface pressure withstood by stearic acid and hence the decrease in compressibility with the increasing X-C60Br24, thereby indicating the domination of C60Br24 characteristics in the mixed monolayers. (c) 2006 Elsevier B.V. All rights reserved.