Background: PIPAC is a novel, laparoscopic intraperitoneal chemotherapy delivery technique which aims to improve on hyperthermic intraperitoneal chemotherapy (HIPEC), ameliorating drug distribution and tissue penetration. Thus far, PIPAC has been conducted with oxaliplatin chemotherapy in Europe, at an arbitrary dose of 92mg/m²; 150mg/m² was found to be intolerable. We conducted a dose-escalation phase 1 study to establish the safety, tolerability and recommended phase 2 dose (RP2D) for PIPAC in Asian patients. Methods: This phase 1 study of oxaliplatin administered via PIPAC was designed as a traditional 3+3 dose escalation study for patients with predominant peritoneal metastasis from a gastrointestinal primary tumor, after failure of standard therapies. Dose levels were planned at 45, 60, 90 and 120mg/m². Repeat doses of PIPAC were permitted, 6 weeks apart. Dose limiting toxicities (DLT) were defined as any clinically relevant grade 3 adverse events occurring within 28 days after PIPAC. Results: This study included 16 patients (25 PIPAC procedures; 8 gastric, 4 colorectal and 1 gallbladder, pancreas and appendix cancer each). Median age was 62 years, with a median peritoneal carcinomatosis index (PCI) score of 17 (range 1 - 39). Two patients developed pancreatitis (grade 2 and 3) on day 6 and day 9 after PIPAC administration at the dose cohort of 45mg/m², necessitating cohort expansion to 6 patients. One patient was noted to have asymptomatic grade 3 hyperamylasemia (90mg/m² cohort). There were no other DLTs and all 3 patients in the highest dose cohort (120mg/m²) tolerated PIPAC well. Nine patients who underwent a 2^nd PIPAC procedure had a decrease in PCI score from 18.4 to 15.5; one patient at 120mg/m² had an improvement in PCI from 30 to 12. Conclusions: The RP2D of PIPAC with oxaliplatin is 120mg/m². Single agent PIPAC is well tolerated, and future studies with PIPAC must consider a bi-directional approach with the incorporation of systemic therapy, with either chemotherapy or immunotherapy to improve efficacy. Clinical trial information: NCT03172416