Abstract Background Hepatitis B virus (HBV) infection is a major public health problem worldwide. More than 2 billion people have been exposed to HBV, and about 257 million individuals are chronic carriers of HBV. HBV reactivation has been increasingly reported in HBV carriers who have undergone immunosuppression or chemotherapy, resulting in mortality. Treatment of hypothalamic/pituitary tumors in HBV carriers requires extensive care to avoid HBV reactivation as steroid therapy is required after surgery for hypothalamic/pituitary tumors. Case presentation This retrospective review identified 5 patients, who were HBV carriers positive for hepatitis B surface antigen among 1352 patients with surgically treated hypothalamic/pituitary tumor in Kohnan Hospital between February 2007 and April 2017. Transsphenoidal surgery was performed with particular attention to prevent damage to the pituitary gland, with delicate manipulation to minimize postoperative steroid coverage. All patients received nucleot(s)ide analogue to control HBV-DNA levels before the surgery. As a result, all patients had a good clinical course. Blood examinations found a transient increase of liver enzymes and HBV-DNA levels in all patients, which started to decrease within 2 weeks after surgery. No specific treatment other than nucleot(s)ide analogues was needed to maintain liver function, and all patients returned to their previous activities including reinstatement. Conclusion Initiation of nucleot(s)ide analogues administration prior to the surgery for hypothalamic/pituitary tumors can be an effective strategy for preventing reactivation in HBV carriers. Appropriate screening of the patient’s HBV phase, optimal timing of nucleot(s)ide analogues -administration, and administration period of nucleot(s)ide analogues need to be established.