Carbon nanotubes (CNTs) are found to inhibit the free-radical cross-linking of vinyl-terminated polydimethylsiloxane (PDMS) by trapping the free radicals in a CNT/PDMS composite. The cross-linking density values measured by swelling test, equilibrium stress-strain test, glass-transition temperature and Raman spectroscopy all decrease with the addition of CNTs. The inhibition effect is shown to be more significant with increased functionality and curvature in the CNTs used. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40355.