The conventional use of expanded vermiculite (EVMT) as an anti-aging modifier for asphalt binders restricts its effectiveness at the asphalt mixture scale because of limited dosage. Therefore, this study investigated the use of EVMT as a substitute filler and evaluated its effects on aging resistance and mechanical performance at the asphalt mastic scale, with the aim of providing insights for optimizing EVMT application strategy and improving its anti-aging efficiency in asphalt mixtures. Conventional limestone (LS) fillers in asphalt mastic were substituted with EVMT at varying volume fractions (0 %, 25 %, 50 %, 75 %, and 100 %). An additional asphalt mastic was also prepared by blending EVMT modified asphalt binder with LS fillers. The differences between EVMT and LS in physiochemical properties were characterized. The effects of quantity and application form of EVMT on aging resistance and other engineering and mechanical properties of asphalt mastic were ascertained. The results indicated that EVMT and LS show significant discrepancies in morphology, structure, and composition. The aging resistance of asphalt mastic is significantly enhanced as the volume percentage of EVMT increases as a substitute filler in asphalt mastic, demonstrating the better heat and oxygen resistances of EVMT relative to LS. Compared to using EVMT as a modifier for asphalt binders, replacing LS with EVMT by the volume fraction of 70 %–100 % proves to be more effective in enhancing the overall engineering performance of asphalt mastic, particularly in terms of aging, rutting, and fatigue distresses. The interplay between filler particles and asphalt matrix is a key factor contributing to the variations in engineering performance observed among asphalt mastics prepared with different amounts and application forms of EVMT. These findings can help guide the optimal utilization of EVMT in the preparation of asphalt mixtures with enhanced long-term durability and mechanical performance.