The properties of antimicrobial peptides adsorbed on inorganic or organic surfaces are of interest for their potential applications in intracellular drug delivery. In this work, continuous-wave (CW) electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) techniques were applied to study adsorption of the short-sequence trichogin GA IV and the medium-length sequence ampullosporin A antimicrobial peptides on the monodisperse colloidal silica nanospheres of 20 nm diameter. The results obtained by CW EPR support the view that the adsorbed peptides form close-packed clusters. PELDOR data show that both trichogin and ampullosporin adsorbed on the silica surface possess a more disordered conformation as compared to that in solution. For ampullosporin, disordering is much more pronounced than for trichogin. After desorption, the peptides restored their conformations; upon adsorption the peptides in some cases may lose partly their biradical character.