Lactic acidosis is an extremely rare paraneoplastic manifestation of hematological malignancies, and often carries an extremely poor prognosis. Mantle cell lymphoma is an aggressive and rare form of non-Hodgkin lymphoma. To the best of our knowledge, it is extremely rare to have severe lactic acidosis in patients with mantle cell lymphoma. In this article, we are reporting a rare case of mantle cell lymphoma diagnosed with typical cluster differentiation (CD markers) in bone marrow examination with persistent lactic acidosis refractory to intravenous hydration that responded well to chemotherapy. Malignant lactic acidosis is a medical emergency that needs rapid evaluation and identification that shows improved prognosis after the introduction of chemotherapy.