The systematic immune-inflammation index (SII) has been used to predict the prognosis of patients with various cancers. This study aimed to determine whether the preoperative SII was associated with postoperative survival among patients with operable colon cancer.This retrospective study included 118 age- and sex-matched healthy subjects and 118 patients who underwent radical surgery for colon cancer between January 2011 and December 2013. The preoperative SII was calculated based on counts of neutrophils, lymphocytes, and platelets in the peripheral blood. Pearson correlation analysis was used to analyze the relationships between the SII and carcinoembryonic antigen (CEA) concentration, average length of stay (ALOS), and medical costs during hospitalization. The χ test or Fisher exact test was used to analyze the relationship between the preoperative SII and the postoperative survival rate.The median SII value was 667.75 among patients with colon cancer, which was higher than the value among healthy subjects. A high SII (>667.75) was associated with a large tumor size and advanced TNM stage, although it was not associated with age, sex, tumor location, or pathological grade. Pearson correlation analysis revealed that the SII was positively correlated with serum CEA concentration, ALOS, and medical costs. Relative to a low SII, a high SII was significantly associated with a lower overall survival rate at 3 years and 5 years after surgery.The present study's findings suggest that the preoperative SII is a useful prognostic index for patients with operative colon cancer.