Maleic anhydride–grafted high-density polyethylene (HDPE; PE-g-MAH) was used to fill the interphase layer of silicon dioxide (SiO₂)/polymethyl methacrylate (PMMA) composites. The mechanical, friction and wear properties of SiO₂/PMMA/HDPE composites were investigated on a ring-on-ring friction and wear tester with AISI 1045 steel metallic ring counterface under dry friction conditions. Scanning electron microscopy (SEM) was utilized to study the worn surfaces of PMMA composites. Experimental results showed that the addition of HDPE decreased the friction coefficient of SiO₂/PMMA composites slightly and reduced the wear volume loss of the PMMA composites obviously. SEM studies indicated that the addition of HDPE could reduce the abrasive wear of SiO₂/PMMA composites. The dispersion of SiO₂ in PMMA composites was also improved.