Rubber crumb derived from the grinding of used truck tread and tyres is used as a low cost filler in rubber compounds based on diene rubber. In order to expand its application to other fields, the surface modification of the rubber crumb could be an interesting and feasible solution. In fact, the surface modification of rubber crumb may be used as a tool to expand its use in applications to compounds with polar rubber matrices or where hydrophilic surface of the rubber crumb could be desirable, for example in water-based dispersion or as filler for asphalt. In the present work, ozone has been used as the active agent to cause surface oxidation and functionalisation of rubber crumb in a fluidized bed reaction. The rubber crumb reacts swiftly with ozone producing CO(2) in the initial stages of reaction and then leading to the desired surface oxidized product. The rate constant of the reaction between ozone and rubber crumb has been determined by FT-IR spectroscopy, monitoring the consumption of ozone in the gas phase in the presence of the crumb. A rate constant value of 5.03 x 10(-3) s(-1) g(-1) of rubber crumb was determined. The degree of the surface oxidation of the rubber crumb can be determined by FT-IR spectroscopy using as reference the intensity of the ketone band at about 1710 cm(-1). Additionally the nominal ratio between the amount of ozone (in mg) reacted with rubber crumb (in g) can be used as a parameter for the degree of the surface oxidation. The surface oxidized rubber crumb shows surface acidity and hydrophilicity. Thermogravimetric analysis, differential thermal analysis and pyrolysis-GC clearly demonstrate that the ozonization of the rubber crumb is directed exclusively to the surface of the crumb and does not affect the bulk properties at all.