Abstract: Objective To assess the efficacy of HyperSGSI gamma knife with different dose fractionations in patients with primary optic nerve sheath meningioma（ONSM）. Methods From Aug. 2004 to Mar. 2010, 22 patients with ONSM were treated with fractionated stereotactic radiotherapy（FSRT） by HyperSGSI gamma knife treatment system. 1 case was treated with conventional fractionation, the radiation dose was 50 Gy in 25 fractions； 21 patients were treated with hypofraction, the radiation dose were 36-40 Gy in 8-12 fractions. Clinical and radiographic followup were performed every 6 months after FSRT therapy， Efficacy of FSRT and improvement of symptoms were evaluated by clinic manifestation and change of tumor maximum diameter in different followup time. Results After a median followup of 25 months，the visual control rate in all patients was 77.3％（17／22）.Visual acuity was improved in 4 patients，remained stable in 13 patients，and deteriorated in 3patients，blindness in 2 patients. The visual control rate would decline with time of follow-up， with one year followup was 95.0％（19／20），with two years follow-up was 75.0％（9／12）. The tumor control rate was 100.0%（22 cases）. The maximum diameter of the tumor was reduced more than 50％ in 8 patients（36.4％）；25％～50％ in 11patients（50.0％）；10％～25％ in 3 patients（13.6％）. The rate of improvement with proptosis was 100.0％（17/17）. The degree of proptosis at pro and post treatment were （17.3±2.7）mm and （14.9±1.5）mm，respectively. There were statistical significance（P＜0.05）. Ten cases with reversible complications could be recovered after symptomatic treatment. Conclusion Fractionated stereotactic radiotherapy can improves tumor control and proptosis for ONSM, while control rate for the visual observation is still needed for a long time. The best dose fractionation with FSRT for ONSM will be required for further study.