The O-2 plasma treatment of self-assembled monolayers (SAMs) of octadecyl mercaptan on gold substrates was investigated as a model for the oxidation of wool fiber surfaces. Three controlled low-pressure gas-plasma treatments were employed in which the active species were (i) atomic oxygen, (ii) atomic oxygen plus vacuum UV radiation, and (iii) full plasma treatment (charged particles in addition to the above). X-ray photoelectron spectroscopy revealed that the plasma treatments differ from each other in the extent of oxidation and etch rate with the full plasma treatment being the most aggressive plasma. The results have confirmed that the charged particles present in a full O-2 plasma treatment are responsible for rapid etching of the organic surface and thus play a significant role in the oxidation mechanism due to radical formation during this process. Vacuum UV radiation also contributes to the oxidation process. Only short plasma treatment is necessary for the oxidation of the lipid layer and the SAM is a suitable model for this process.