Objective: To evaluate the therapeutic efficacy of low-grade glioma (WHO grades I-II) patients treated with gamma knife radiosurgery and study on the efficacy evaluation method and radiobiological effect. Methods: 140 MRI data of 52 patients after gamma knife radiosurgery were analyzed in tumor size, necrosis or cyst formation, radiation-induced edema and MRI contrast enhancement and circumsciption change for therapeutic efficacy was evaluated. Results: The efficiency rate was 84.3%. The salient efficiency rates were 54.3% for total and 30%, 36.4%, 50%, 68%, 69.2%, and 73.1% for seg-menting, respectively. Aggrandizement of tumor related to MRI contrast enhancement and necrosis or cyst formation. Radia-tion-induced oedema occurred for 32.7%. The MRI contrast enhancement occurred for 57.7% and showed special lace-like ring while some piece-like. Conclusion: Evaluation by MRI has showed gamma knife radiosurgery is efficient for low-grade glioma. The segmenting salient efficiency rate that increase with time is better for evaluation than the efficiency rate especially for long-term MRI follow-up. Radiobiological effect affect the efficacy evaluation. MRI contrast enhancement appears after therapy and shows special as lace-like ring and partly minificates or vanishes subsequently. Objective: To evaluate the therapeutic efficacy of low-grade glioma (WHO grades I-II) patients treated with gamma knife radiosurgery and study on the efficacy evaluation method and radiobiological effect. Methods: 140 MRI data of 52 patients after gamma knife radiosurgery was analyzed in tumor size, necrosis or cyst formation, radiation-induced edema and MRI contrast enhancement and circumsciplinary change for therapeutic efficacy was. Results: The efficiency rate was 84.3%. The salient efficiency rates were 54.3% for total and 30%, 36.4% Aggrandizement of tumor related to MRI contrast enhancement and necrosis or cyst formation. Radiographic-induced oedema occurred for 32.7%. The MRI was for 57.7% and showed special lace-like ring while some piece-like. Conclusion: Evaluation by MRI has showed gamma knife radiosurgery is efficient for low-grade glioma. The segmenting salient efficiency rate that increase with time is better for evaluation than the efficiency rate especially for long-term MRI follow-up. Radiobiological effect affect the efficacy evaluation. MRI contrast enhancement appears after therapy and shows special as lace-like ring and partly ministered or vanishes subsequently.