Abstract： Objective To evaluate the applicability of low-field intraoperative magnetic resonance imaging during transsphenoidal micresurgery of pituitary macwadenormas. Methods Tmnsnaso-sphenoidal resection of 82 pituitary macroadenomas(modified Hardy(s) grade II to IV)were performed under the guidance of real-time updated images acquired by 0.15 Tesla PoleStar N-20 iMRI In comparison with early(within 72 h)postoperative highfield MR images,the accuracy of imaging evaluation of low-field iMRI was analyzed. The definitive benefits as well as major drawbacks of low-field iMRI and its influence on transsphenoidal surgery were assessed with respect to tumor resection control and clinical outcome.Results Intraoperative imaging revealed residual tumors in 29 of 82 cases and led to extended resection in 25 cases.Complete resection was achieved in 16 Patients. As a result.the percentage of gross total removal of macroadenomas was increased from 61.0% to 81.7%.The accuracy of imaging evaluation of low-field iMRI was 86.6% ,compared with early postoperative hish-field MRL A significantly lower accuracy(53.3%)was identified in those cases with cavernous sinus invasion in contrast to 94.0% found in other sites(P<0.001).There was no iMRI-related complication.Conclusions Intraoperative magnetic resonance image-based navigation provides objective information for the guidance of surgical procedure and the real-time jedgment of surgical consequence,which leads to higher percentage of tumor removal and better clinical outcome in transsphenoidal Surgery for pituitary macroadenomas.