Based on current evidence and controversy above, we designed this non-inferiority, phase 3 clinical trial to explore the optimal dosage of capecitabine monochemotherapy for stage II/III elderly CRC patients. Following the results of sample size estimation, 710 postoperative (pT3-4NanyM0 or pTanyN+M0) elderly patients between 70 to 90 years of age were anticipated to be included and randomly divided into two groups (A and B). Patients in group A would receive the standard dose regimen (1,250 mg/m2 twice daily on days 1-14, and repeated on day 22); accordingly the patients in group B would receive the reduced dose regimen (1,000 mg/m2 twice daily on days 1-14, and repeated on day 22). The primary endpoint was 3-year disease free survival (DFS), other outcomes included 3-year overall survival (OS), completion rate, toxic and adverse effects and quality of life (Qol).