The paper describes conductometric quantitative determination of thiol- and sulfonic acid groups on organosilica surface with immobilized layer of partly-oxidized mercaptopropyl groups. A set of MCM-41 type samples containing 1 mmol g-1 of mercaptopropyl groups was oxidized with proportional quantitates of hydrogen peroxide and subsequently was characterized with different ratio of grafted mercaptopropyl and propylsulfonic acid groups. The data calculated from conductometric titration were approved by collation with corresponding XPS spectra, which demonstrate linear correlation of results of both technique. The described method was applied to reveal ambient oxidation of organo-silicas with immobilized thiol groups.