Nanometer-sized xonotlite fibers have great potential application in many fields. The traditional method of preparing ultra fine xonotlite fibers uses the ultra fine and highly active silica as the major raw materials, which is not only expensive but also difficult to prepare the xonotlite fibers with diameters around 100 nm. In this study, the ultra fine xonotlite fibers with diameters around 100 nm were prepared by an autoclaving method. The preparation was low-cost oriented by using natural powder quartz and lime as the major raw materials. The intergrowth of the fibers formed thin shell hollow balls or ellipsoids, namely the secondary particles.The length of the nanometer-sized xonotlite fibers was around several microns. The fibers and their secondary particles were produced at 216℃ for 6 h with a continuous stirring of 300-500 r/min. Zirconium oxychloride was used as an additive. The experiments show that zirconium oxychloride has an enormous effect on the growing habit of xonotlite crystals and plays an important role in controlling the diameter of the xonotlite fibers.