Background: Appendiceal adenocarcinomas (AAs) are a rare and heterogeneous mix of tumors for which only few preclinical models exist for drug discovery. These tumors are commonly treated with chemotherapy like those for colorectal cancer despite clear evidence that the two cancers are distinctly different in their clinical behavior and molecular profiles. Taxanes such as paclitaxel (PTX) and docetaxel have been used in the systemic treatment of gastric cancer with peritoneal metastases. IP administration of PTX has been considered a promising treatment for eliminating peritoneal metastasis, as IP delivery of PTX can attain a higher drug exposure in the peritoneal cavity with reduced systemic toxicity because of high local concentrations over a long period of time due to its hydrophobic property. The purpose of this study was to test the efficacy of IP PTX treatment in orthotopic AA PDX models. Methods: AA tumors TM00351, PMP-2 and PMCA-3 were implanted in the peritoneal cavity of NSG mice. PDX models were treated with PTX (6.25, 12.5 or 25.0 mg/kg, IP) with weekly (3 weekly treatments and 1 week off, for two cycles) or biweekly (biweekly treatments for up to 12 weeks) schedule. The peritoneal tumor burden was monitored by MRI. Solid tumor size was evaluated by modified peritoneal Response Evaluation Criteria In Solid Tumors (mpRECIST) method using ImageJ software and mucinous tumor volume was quantified by OsiriX Lite software. Results: TM00351, taken from a high-grade tumor (Grade 3), formed mucin-rich solid tumors with mucinous ascites. PDX models PMP-2 (Grade 2) and PMCA-3 (Grade 3), both with GNASR201C mutation, had a mucinous phenotype similar to GNAS mutant appendiceal tumors in humans. Weekly 25.0 mg/kg of IP PTX treatment reduced AA tumor growth of TM00351 (77.9% reduction vs. control), PMP-2 (98.6% reduction vs. control), and PMCA-3 (85.6% reduction vs. control). Similarly, biweekly 25.0 mg/kg of IP PTX treatment was effective on PMCA-3 (66.2% reduction vs. control). Survival of PMCA-3 PDX mice was significantly improved by 12.5 mg/kg (p=0.0254, log-rank test) and 25.0 mg/kg (p=0.0038) of IP PTX. At 25.0 mg/kg IP PTX treatment induced 12.0% body weight loss of PMCA-3 PDX mice 1 week after the treatment. Lower doses of IP PTX treatment, 6.25 and 12.5 mg/kg, did not induce significant body weight loss or any noticeable adverse effects on mice. Comparing the efficacy of IV to IP administration, neither 6.25 or 12.5 mg/kg of IV PTX reduced growth of PMCA-3, 25.0 mg/kg of IV PTX was lethal to mice shortly after administration. Conclusions: IP PTX is a therapeutically active for mucinous AA tumors.