Complication of leptomeningeal carcinomatosis (LMC) is critical. It causes rapid neurological deterioration, and subsequently, discontinuation of the ineffective treatment even in body tumor dormancy. Large molecular chemotherapeutic agents that are unlikely to penetrate the CSF space, are more likely to not treat LMC, typically in chemo-sensitive tumors. With the introduction of novel regimens, significant advances in overall survival have been observed even in formerly chemo-resistant tumors, such as pancreatic cancer. Although such cases are still rare, the number of pancreatic cancer patients complicated with LMC are increasing, and this therefore needs more recognition. A 49-year-old woman was diagnosed with stage IVa pancreatic cancer. She underwent surgery, and subsequent adjuvant chemotherapy. After three lines of chemotherapy over a 3-year period, where the body disease remained dormant, the patient was complicated by LMC. The diagnosis was made 4 months after the onset of headache. The patient received intrathecal methotrexate treatment but succumbed shortly after treatment induction. Pancreatic cancer is still relatively chemo-resistant and is one of the least likely types of tumor to be complicated by LMC due to patients dying of the primary tumor. Advancements in treatments have led to a prolonged period of primary tumor control, but not in the CNS due to the poor penetration of chemo-agents to this site. The present case seems to be a typical result of modern era anti-cancer therapy. Therefore, we emphasize the necessity of earlier recognition of this complication so that we can initiate specific treatment targeting the CSF space, especially in this formerly chemo-resistant tumor in order to improve its prognosis.