AbstractNanocomposites, and in particular, Polymer–Fullerene blends, have recently drawn strong attention owing to their properties and their numerous applications in new‐generation electronic and optoelectronic devices. The fullerene concentration in the material is critical since it dictates its electrical behavior. In this context, precise knowledge of the fullerene depth distribution in the blends is needed. Here, we investigate the capability of the ToF‐SIMS technique to provide quantitative information on PMMA‐C60 blends with extremely small C60 concentrations. Smooth PMMA layers of ∼130 nm thickness ranging from 0 to 0.04 wt% C60 were deposited on Si wafers. Samples were analyzed with an ION‐TOF TOF SIMS V instrument in negative mode. Using low‐energy Cs+ sputtering (250 eV) and Bi3+ as the analysis ion allowed monitoring of C60 characteristic secondary ions, namely C60− and its isotopes at m = 720,721,722,723,724,725 u. Operating the beams in noninterlaced mode enabled successful depth profiling of samples with very little signal decay. Improvement of depth resolution was achieved by cooling the sample while profiling; AFM study of crater bottoms showed reduced roughness at low temperature, justifying the improvement. Segregation in depth of C60 against PMMA was not observed, in agreement with surface free energy values determined by a contact angle method. Point‐by‐point normalization of C60 signal (C60−, m = 720 u) to PMMA monomer signal (C5H9O2−, m = 101 u) was found to give a linear function of C60 concentration with excellent regression coefficient. Copyright © 2010 John Wiley & Sons, Ltd.