Three polyhedral oligomeric silsesquioxanes (POSS) were used together with silica as fillers or modyfing agents for hydrogenated butadiene-acrylonitrile rubber to improve the properties of the rubber vulcanizates produced by using (PhCMe2O)(2) curing agent. The vulcanizates were aged at 50-70 degrees C for 200 h optionally under UV irradn. The addn. of POSS resulted in an increase of interfacial interactions in the vulcanizates and in an increase in their tensile strength. The stabilizing effect of POSS was confirmed by high ageing coeffs.