The use of simple ferrocene/ferricenium couple in electrochemical sensors and other devices is limited because of its instability in aqueous media. However certain modified ferrocenes are found to be relatively stable and hence are attractive alternatives for the applications. This paper describes the electrochemistry of 11-ferrocenyl-1-undecanethiol (FcC11SH) in sulphuric acid media, which is investigated by cyclic voltammetry of thin films of the material derivatised on gold substrates. It has been found that the oxidation and reduction peak potentials are independent of H+ concentration in the pH range 2-10. However, the peak potentials change linearly with sulphuric acid concentration in the range 1-5 M. Extended cycling of the material indicated that, under the conditions of the experiment, FcC11SH was more stable than the simple ferrocene, and may be suitable for potentiometrically monitoring H+ concentration in concentrated sulphuric acid solutions.