The present invention relates to a composition acting as coupling agent between fillers and peroxidically crosslinking elastomers in rubber compounds, which comprises, as component comprising silicon compounds, a mixture a) of vinylalkoxysiloxanes with alkylalkoxy-siloxanes, or b) of vinylalkoxysiloxanes with phenylalkoxy-siloxanes, or c) of vinylalkoxysiloxanes with phenyl/alkyl-alkoxysiloxanes or d) of acrylic or methacrylic alkoxysiloxanes with alkylalkoxysiloxanes, or e) of acrylic or methacrylic alkoxysiloxanes with phenylalkoxysiloxanes, or f) of acrylic or methacrylic alkoxysiloxanes with phenyl/alkylalkoxysiloxanes, or g) of at least one co-oligomeric organosiloxane which, as organofunctional groups, bears at least one group from the series vinyl, acrylic and methacrylic, and at least one group from the series alkyl and phenyl, and at least one alkoxy or hydroxy group. The present invention further relates to the use of a composition of the invention as a coupling agent in filled and peroxidically crosslinking rubber compounds, to rubber compounds obtained in this way, and to items made therefrom.