Background: Peritoneal carcinomatosis in colorectal cancer is an advanced stage of the disease where improved survival can be attained whenever the resection associated with hyperthermic intreperitoneal chemotherapy is possible. In unresectable cases, systemic chemotherapy is administered to obtain conversion to resectability but results have not yet been clearly evaluated. Local chemotherapy in this setting has been proven useful in several similar situations. The aim of the present pilot study was to evaluate the feasibility of pre-operative intraperitoneal chemotherapy with oxaliplatin in these patients. Methods: Six patients with unresectable peritoneal disease of colorectal origin were included in the study. An intraperitoneal implantable chamber catheter was inserted during the laparotomy that evaluated the extent of the peritoneal disease (peritoneal carcinomatosis index 25 to 39). Patients then underwent intraperitoneal chemotherapy with oxaliplatin 85 mg/m2 in combination with systemic chemotherapy (FOLFIRI or simplified LV5FU) and a targeted therapy every 2 weeks. Results: Two catheter perfusion incidents were reported due to the abdominal wall thickness. Two patients completed the four intraperitoneal (IP) chemotherapy cycles without major toxicity. One patient developed grade 3 or 4 diarrhea requiring a short intensive care unit (ICU) stay, though it is not clear whether the event was induced by intravenous irinotecan, IP oxaliplatin or the combination of both. Grade 3 fatigue and abdominal pain were also recorded. For one patient with aggressive disease, best supportive care was initiated after the first course of chemotherapy. Conclusions: Our study is the first to assess intraperitoneal oxaliplatin-based chemotherapy in the preoperative setting for patients with unresectable peritoneal metastases. The tolerance was acceptable for 85 mg/m2 IP oxaliplatin combined with systemic therapy in these patients. Our results justify carrying on with a phase I/II trial to determine the recommended dose of oxaliplatin in this clinical context and its efficacy.