Process of producing unvulcanized rubber useful for producing vulcanized rubber with improved hysteresis, which comprises mixing a composition comprising unvulcanized rubber, carbon black and xanthogen polysulfide at an elevated temperature in a non-productive stage and composition suitable for producing unvulcanized rubber useful for producing vulcanized rubber with improved hysteresis, which comprises unvulcanized rubber, a filler comprising carbon black and xanthogen polysulfide.