Objective: To evaluate the effect of tumor-stroma ratio (TSR) on disease progression and prognosis of pseudomyxoma peritonei (PMP) from the appendix.Methods: The study included 30 PMP patients with complete individual patient data, who underwent cytoreductive surgery (CRS) plus hyperthermic intraperitoneal chemotherapy (HIPEC) in Beijing Shijitan Hospital. Image-Pro Plus was used to quantitatively analyze the proportion of tumor and stromal areas in hematoxylin-eosin staining pathological images, from which TSR was derived. Correlation studies were conducted to evaluate the relationships between TSR and clinicopathological features, immunohistochemical characteristics, and prognosis of PMP.Results: Among 30 PMP patients, there were 16 males (53.3%) and 14 females (46.7%), with the mean age of (54.9±2.3) years. There were 15 cases (50.0%) of low-grade mucinous carcinoma peritonei (LMCP) and high-grade mucinous carcinoma peritonei (HMCP), respectively, with vascular tumor emboli occurring in 4 cases (13.3%), nerve invasion occurring in 3 cases (10.0%), and lymphatic metastasis occurring in 4 cases (13.3%). The median peritoneal cancer index (PCI) score was 36 (range: 3-39). The median TSR was 8% (range: 2%-24%), with TSR≤10% in 19 cases (63.3%) and TSR>10% in 11 cases (36.7%). Immunohistochemistry showed that 16 cases (53.3%) had Ki67 label index ≤ 50% and 14 cases (46.7%) > 50%. The mutation rate of p53 was 56.7% and the loss rate of MMR protein was 11.8%. In addition, the expression rates of MUC2, MUC5AC, CDX2, CK7, and CK20 were 66.7%, 100.0%, 82.6%, 56.0%, and 92.3%, respectively. There were significant correlations between TSR and histopathological types, nerve invasion, Ki67 label index, and p53 mutation (P<0.05 for all). At the end of the last follow-up, 21 patients (70.0%) died and 9 patients (30.0%) survived, including 6 patients survived with tumor. The median overall survival (OS) was 12.7 months (95%CI: 10.4-11.5 months), and the 1-, 2-, and 3-year survival rates were 60.5%, 32.3%, and 27.7%, respectively. The median OS was 19.4 months (95%CI: 3.0-35.9 months) in the TSR≤10% group, versus 12.6 months (95%CI: 0.7-24.5 months) in the TSR>10% group (χ ²=3.996, P=0.046).Conclusion: TSR is correlated with histopathological types, tumor proliferation, invasion behaviors and prognosis of PMP, thus could be a new prognostic indicator for PMP.