Background: To evaluate factors affecting the delay ( ≥ 8 weeks) of AC and the impact of chemotherapy delay on survival in patients with colon cancer(CC). Methods: The study cohort consisted of patients with stage II and III colon cancer, diagnosed between January 1, 2011 and December 31, 2012, who underwent curative resection and AC at all hospitals registered in the Korean Health Insurance Review and Assessment Service (HIRA). Detailed clinical data are from monitoring and evaluation of quality of colon cancer care. Results: Among 5355 patients, 154 (2.9%) received AC more than 8 weeks after surgery. Based on multivariate analysis, risk factors associated with AC delay ≥ 8 weeks were: older age [65 to 74 years (hazard ratio, HR = 1.48) and 75 years (HR = 1.69), p = 0.0354], medical aid status in health security system (HR = 1.76, p = 0.0345), emergency surgery (HR = 2.43, p = 0.0002), and chemotherapy with fluoropyrimidine (HR = 1.49, p = 0.0373). Independent prognostic factors for inferior OS included AC delay ≥ 8 weeks (HR = 1.49, p = 0.0365), older age [65 to 74 years (HR = 1.94) and 75 years (HR = 3.41), p < 0.0001], TNM III stage (HR = 2.46, p < 0.0001), emergency surgery (HR = 1.89, p < 0.0001), ASA score with 3 or higher (HR = 1.50, p < 0.0001), and higher transfusion amount (HR = 1.09, p = 0.0392). OS rates in patients with stage II / III CCs according to delay of AC using 8 weeks cutoff showed inferior OS in the delayed chemotherapy group (p = 0.008).Detailed OS rates were 97.81% at 1 year, 93.77% at 2 year, 89.62% at 3 year, and 85.79% at 4 year in the chemotherapy group within 8weeks. In the delayed chemotherapy group ≥ 8 weeks, OS rates were 96.1% at 1 year, 87.66% at 2 year, 80.98% at 3 year, and 80.2% at 4 year. Conclusions: This national population-based cohort study shows that delayed commencement of AC, defined as ≥ 8 weeks, is associated with inferior OS in CC patients with stage II / III. To reduce the proportion of patients receiving delayed AC, multidimensional aspects such as health insurance status or age should be considered. Based on our results, the time of commencement of chemotherapy can be incorporated as another quality indicator for colon cancer care.