Abstract: Pseudomyxoma peritonei (PMP) is a rare malignant peritoneal syndrome characterized by progressive intra-abdominal accumulation and redistribution of gelatinous tumor-derived mucins. This disease primarily originates in the appendix or ovaries and exhibits distinct biological behavior and clinicopathological features. Carbohydrate antigen 19-9 (CA19-9), a critical tumor biomarker, is significantly correlated with the development and progression of PMP. This association renders CA19-9 increasingly valuable in clinical diagnosis and treatment. Furthermore, molecular biological characteristics of CA19-9, including structural properties, biosynthetic pathways, and mechanisms in mediating tumor metastasis, are systematically elaborated. These findings highlight the association between CA19-9 expression and PMP pathological grading, clinical prognosis, and therapeutic response monitoring. Additionally, the study thoroughly analyzed the synergistic role of CA19-9, alongside other tumor biomarkers, in PMP management. Based on current evidence, future research directions are proposed. These include the potential application of CA19-9 in early PMP diagnosis, its therapeutic utility as a molecular target, and the exploration of CA19-9-associated signaling pathways in PMP pathogenesis. The insights provide novel perspectives and a theoretical foundation for PMP-based precision medicine.