In the paper, ultrafine quartz, sericite and wollastonite modified with silane coupling agents KH-570 were incorporated into natural rubber(NR). The synergisitc effect on reinforcing NR caused by the three types of fillers was investigated under a same vulcanizing formulation and process. The mechanical properties and microstructure of the vulcanizates were conducted through mechanical testing and scanning electron microscopy(SEM). The results of mechanical properties tests showed that when one of these three fillers was loaded within NR alone, the tear strength and permanent set of NR vulcanizates filled with quartz could reach 27.61 kN m-1 and 16.0%, respectively, stress at 300% elongation of NR vulcanizates filled with sericite could attain 4.69 MPa, and the tensile strength and elongation at break of NR vulcanizates filled with wollastonite could get to16.64 MPa and 951.21%, respectively. Under the condition that the filler loadings were 40 parts per hundred parts of rubber(phr), and the mass ratio of quartz, sericite, wollastonite was 1:1:3, the tensile strength and tear strength could come up to 17.33MPa and 27.54 kN m-1. The mechanical properties of NR composites filled with mixtures were found to be complemented by those three types of minerals. SEM results revealed that the fillers are well dispersed in the rubber matrix in the parallel arrangement with a densest stack, and the synergistic reinforcment effect of the fillers on NR was obvious.