With natural minerals as raw materials, silicone rubber reinforcement fillers, namely the modified ultrafine powders with excellent properties, are prepared through ultrafine crashing, surface chemical modification and mechanical chemical modification. The reinforcement properties of the products are close to those of fumed silica, and can be used in silicone rubber to replace part of fumed silica. 1. Preparation of ultrafine powders Four kinds of natural minerals, viz. talc, quartz, needle wollastonite and grained wollastonite, are crashed into powder and, if necessary, purification, fractionation and demoisturing should be carried out to obtain powders finer than 43μm(325 mesh) with moisture content lower than 5%. Then, these powders are processed in a QS-50 micronizer, where they become ultrafine powders with the average particle size smaller than 2μm. Theparticle size distribution and specific area are presented in Table 1. It is obvious that under the same processing condition, the change of particle size and specific area of a mineral powder differs from that of other kinds of mineral powder. 2. Preparation of surface chemical modifying filler The mixture of mineral powder and coupling agent is treated in the GH_10 high speed mixer to prepare surface modified powder, with the temperature controlled at 120℃. The mechanism of surface chemical modification is studied by means of IR spectra of quartz powders and the determination of reinforcement effect of modified quartz powder in silicone rubber. It is pointed out that OHgroup concentration on the surface of sintered quartz becomes so small that the surface modification can not take place effectively. The surface energy of mineral powders before and after chemical modification is also determined and approached. 3. Mechanical chemical modification Mechanical force makes mineral particles crashed, with the new surface having larger surface activity. This makes mineral powder easy to react with the coupling agent and to be modified. In the experiment, the coupling agent (B_5) is mixed with mineral powders and thneral products are determined and presented in Table 4. It is pointed out that under the same processing condition, different kinds of minerals obtain different effects of modification. The larger the quanity of coupling agent used, the greater the decrease of surface energy and the increase of specific area.