 This is a single arm phase II trial with combined celecoxib, tegafur-uracil, folinate and preoperative radiotherapy for patients with locally advanced rectal cancer. The primary end point is pathological complete response pCR rate. The secondary endpoints are toxicities of combined celecoxib and chemoradiation, negative resection margin rate, clinical tumor response by magnetic resonance imaging MRI, sphincter preservation rate, disease-free survival and overall survival. 