Background and Aims Intrahepatic cholangiocarcinoma (ICC) is a highly malignant tumor with poor prognosis. Surgical resection is the preferred treatment in clinical practice, but patients often experience high rates of postoperative recurrence. the incidence of ICC has been steadily increasing over the past 30 years. Tumor size, as an important prognostic factor, significantly affects the survival outcomes of patients. This study was conducted to investigate the impact of tumor size on the prognosis of patients with solitary ICC after radical resection, so as to provide more accurate prognostic assessment for clinical decision-making.Methods The clinicopathologic data of 654 patients who underwent radical resection and were pathologically diagnosed with ICC between December 2011 and December 2017 in 13 hospitals across China were retrospectively analyzed. Cox regression analysis was used to identify prognostic factors for ICC patients, Kaplan-Meier method was used to plot survival curves, and Log-rank test was used to compare overall survival (OS) differences among patients with different tumor sizes.Results A total of 307 patients were included. There were 40 cases (13.03%) with tumor size ≤3 cm, 177 cases (57.65%) with tumor size >5 cm, and 90 cases (29.32%) with tumor size >3-5 cm. Cox regression analysis revealed that margin status, pathological lymph node status, satellite nodules, and tumor size >5 cm were independent risk factors for the prognosis of solitary ICC patients (all P<0.05). The 1-, 3-, and 5-year OS rates for patients with tumors ≤3 cm were 83.3%, 73.8%, and 54.7%, for patients with tumors >3-5 cm were 81.1%, 40.7%, and 36.1%, and for patients with tumors >5 cm were 72.1%, 37.7%, and 29.0%, respectively (P=0.021). Patients with different tumor sizes were grouped and compared based on whether lymph node dissection was performed. The results showed that in ICC patients with tumor size ≤3 cm, there was no significant difference in OS rate between the two groups (P=0.780); in patients with tumor size >3-5 cm, those not undergoing lymph node dissection had significantly higher OS rate than those undergoing lymph node dissection (P=0.017); in patients with tumor size >5 cm, those who underwent lymph node dissection had significantly higher OS rate than those who did not (P=0.025).Conclusion In patients with solitary ICC, those with tumors ≤3 cm have a relatively better prognosis. For patients with solitary ICC and tumors >5 cm, lymph node dissection surgery is recommended.