Process for surface activation and/or devulcanization of sulfur-vulcanized rubber particles. In order to break the sulfur bridges and to reduce the sulfur, the rubber particles are treated in a biotechnological manner in a medium with mesophilic anaerobic and/or optionally anaerobic and/or microaerophilic bacteria and/or with one or more enzyme systems of such bacteria. The thus-treated activated rubber particles show improved vulcanization properties in comparison with non-treated rubber particles, and permit the production of better quality articles.