Primary hepatic lymphoma is a very rare condition, and the majority of the cases reported are of B-cell origin. We report a case of a 65-year-old man with primary hepatic peripheral T-cell lymphoma, not otherwise specified (PTCL-nos) who presented with 15% weight loss and general fatigue over the previous 9 months. Imaging studies and bone marrow examination could not confirm a diagnosis of lymphoma. Liver biopsy was performed because of an elevated soluble interleukin-2 receptor (sIL-2R) level (17,000 U/I) and hepatomegaly. After the diagnosis of primary hepatic PTCL-nos, treatment with low-dose corticosteroid was initiated, and the sIL-2R level decreased. Discontinuation of corticosteroid treatment resulted in the re-elevation of the sIL-2R level, and subsequently, treatment with low-dose corticosteroid was reinitiated. The sIL-2R level decreased rapidly, and the patient is alive with no evidence of lymphoma for 50 months after diagnosis. Thus, we found that a low-dose corticosteroid was effective in the long-term control of the disease, whereas many previous studies reported that primary hepatic PTCL-nos has a poor prognosis.