Background: Adjuvant chemotherapy in patients with high-risk stage II and III colorectal cancer prevents recurrence by eliminating minimal residual disease. However, patients who are at high risk of recurrence after completing standard adjuvant therapy are currently unknown. Although ascites CEA level has been associated with long-term oncologic outcomes, the clinical significance of ascites CEA in high-risk stage II and stage III colorectal cancer (CRC) has not yet been described. The present study aimed to determine the long-term oncologic impacts of ascites CEA level after curative colorectal cancer. Methods: A total of 191 patients with stage II/III CRC were included in this study, between January 2015 and December 2018. CEA of peritoneal fluid sampled at the beginning of each operation was analyzed. long-term oncologic outcomes were analyzed with the known risk factors for recurrence in CRC. Results: Multivariate analysis of recurrence revealed that lymphatic invasion (HR 6.0, 95% CI 1.1–32.0, p = 0.04), vascular invasion (HR 2.9, 95%CI 1.0–8.0, p = 0.04), mucinous cancer (HR 5.5, 95% CI 1.6–18.4, p = 0.006), and peritoneal fluid CEA above 5 ng/dl (OR 4.2, 95% CI 1.2–15.0, p = 0.008) were significant risk factors (Table). Peritoneal fluid cytology, microsatellite instability, cancer obstruction did not significantly impact DFS in stage II/III CRC. There were 14 patients with liver metastasis, among them, 11 patients without peritoneal metastasis; they had high ascites CEA level. While 8 patients had lung metastasis, 7 of them confirmed high ascites CEA levels. Conclusions: Our results indicate that the ascites CEA may predict as an important biomarker to identify those at risk of distant metastasis in high-risk stage II and stage III CRC patients. We suggest ascites CEA analysis might be included in patient risk assessments and oncologic prediction tools.