Abstract A range of ground rubber (GR)/acrylonitrile–butadiene–styrene (ABS) composites were developed that contained untreated and various treated rubber particles. The tensile properties of the composite materials were significantly improved over the untreated GR/ABS sample either by a two-step treatment process involving surface chlorination of the GR followed by grafting of either amine-terminated butadiene acrylonitrile (ATBN) or triethanolamine zirconium chelate (TEAZ) molecules, or via in situ compatibilization of the chlorinated GR (Cl-GR) and the ABS matrix with the addition of up to 2% of Lewis acid catalysts such as AlCl 3 , FeCl 3 , or ZnCl 2 . In comparison with the properties of the untreated GR/ABS composite, the two-step treatment provided an increase of up to 18% in tensile strength, 17% in Young’s modulus, and 83% in tensile toughness, whilst the in situ compatibilization approach led to increases in these properties of up to 46%, 33%, and 217%, respectively when 2 wt% AlCl 3 was added during the compounding stage of the composites. The tensile properties of the different GR/ABS composites were determined in accordance to the Australian Standard 1145–1989, whilst the surface chemistry of the untreated and surface-treated GR was characterized by X-ray photoelectron spectroscopy (XPS).