It now has been found that the properties of filled rubber compositions comprising rubbers having an unsaturated carbon chain can be improved by including therein, a minor property-improving amount of at least one 1,3-dihydroxy-benzimidazolinone or derivative compound of the formula ##STR1## wherein R is hydrogen, or a halogen, hydroxyl, lower hydrocarbyl, lower hydrocarbyloxy, lower hydrocarbylthio, lower hydrocarbyl nitrile, carboxyl, cyano, nitro, amino, amide or --C(O)--R'" where R'" is an aryl or a lower hydrocarbyl group; each R' independently is H, lower alkyl, acyl, CONR"2 or CONHR" where R" is alkyl or aryl. When vulcanizates are prepared from such uncured rubber compositions, the vulcanizates exhibit reduced low strain hysteresis and a high electrical resistivity.In another aspect of the invention, a filled vulcanizate made by vulcanizing uncured compositions of the type described above and containing a filler, particularly carbon black, is improved in filler interaction, hysteresis, modulus, compression set and resiliency. Rubber articles and portions thereof such as tires, hoses, belts, springs, tread, sidewalls and the like can be made utilizing the improved filled vulcanizates of the invention.