With the TEM and physical gas adsorption techniques, porous properties of nano-fibriform silica (MLD: 92.73 %) from natural chrysotile are studied in this paper. The results indicate that porous nano-fibriform silica results from brucite octahedral sheets of nature chrysotile dissolved completely and Si-O tetrahedral sheets collapsed by acid leaching. Its length is at a micron or nanometer scale.There are two types of pores: pores among neighboring fibers and pores in nanofiber. These pores (less than 6.5 nm in diameter, mostly 2.1 nm and 3.8 nm) all belong to mesopores. The pores in fibers consist of those among SiO2 particles, those among aggregates, remnant nanotubes and capillary tubes. Nanofibriform silica proves better than the traditional silica as a carrier of catalyzer and a filler for reinforce rubber and plastics.