A range of mesoporous solid sulphonic acid catalysts have been prepared from a mercaptopropyl-trimethoxysilane (MPTS) precursor by sol-gel synthesis. The creation of surface sulphonic acid functionality via thiol oxidation has been followed by XPS and Raman spectroscopy. It is possible to continuously vary the sulphonic acid loading from 1 to 12 wt.% while maintaining pore volume and mesostructure. The resulting materials exhibit high thermal stability and acid strength across the composition range and show good activity and selectivity in esterification and condensation reactions.