Objective To investigate MR features and pathological characteristics of the pilocytic astrocytoma (PA). Methods MR imaging and post-operative pathological data of 17 patients with PA were analyzed retrospectively. Results Among these 17 cases of PA, the tumors were supratentorial in 5 and infratentorial in 12. 11 cases were large cystic with nodule type, 4 cases were solid mass type, and 2 cases were purely cystic type．In MR image, lesions were sharply demarcated with 1ittle or no surrounding edema.The cystic liquid exhibited long T1 and long T2 signal except 1 case of intratumoral hemorrhage. The solid part or nodule showed slightly low signal on T1WI, slightly high signal intensity on T2WI and could be significantly enhanced. The wall of cyst was smooth, could be significantly enhanced or non-enhanced. Microscopical study: PA characteristically contained alternative densely packed areas and loosly packed areas. The tumor cells had elongated hair-like cytoplasmic processes. Rosenthal fibels varying in amount from a few to substantial could be found and were particularly common in the fibrillary area. The loose tissues were composed of minute vacuoles and microcysts. Tumor cells expressed GFAP. Conclusion Accurate comprehension of MR features and pathological characteristics of the PA is beneficial for pro-operative daignosis．