Abstract: Objective To evaluate the feasibility,safety and efficacy of preoperative intensity-modulated radiotherapy （IMRT） with oral xeloda in patients with locally advanced mid/low rectal cancer using a simultaneous boost technique. Methods From August 2012 to May 2013,a total of 19 consenting operable patients with stageⅡ or Ⅲ adenocarcinoma of the rectum admitted to the First Medical Center of Chinese PLA General Hospital were enrolled in this study.All patients received xeloda （825 mg/m² po bid,5 days/week for 5 weeks）,and IMRT 50 Gy （2.0 Gy/fraction） was performed in 25 fractions to the pelvic lymph node stations with a simultaneous integrated boost （SIB） of 56.25 Gy （2.25 Gy/fraction） to the rectal tumor and pelvic lymph node metastasis in 25 fractions.All patients were planned to receive a total mesorectal excision after the completion of CRT 6-10 weeks later.Pathological complete response rate （pCR）,sphincter preservation rate,overall survival （OS）,local recurrence rate （LRR）,distant metastasis rate （DMR） and disease-free survival （DFS） were the primary endpoint.The secondary endpoints included acute and late toxicity,tumor down-staging rate and postoperative complication. Results The age of 19 patients ranged from 34 to 70 years old,with a median age of 57 years,and there were 3 females and 16 males.All patients completed a full-dose chemoradiotherapy as planning and then went on to surgical resection.The majority short-term and long-term adverse reactions were grade 1 or 2,and no grade 3-4 adverse event was observed.pCR rate was 21.2% （4/19）,the sphincter-preserving rate was 73.3% （14/19）,the tumor downstaging rate was 66.7% （20/30） and the R0 resection rate was 100%.Postoperative complications incidence rate was 15.8% （3/19）,including 1 case of adhesive intestinal,1 case of obstruction delayed wound healing and 1 case of rectovaginal fistula.The 3-year OS,LRR,DMR,DFS were 94.4% （17/18）,5.1% （1/18）,0,94.4% （17/18）,respectively,and they were 88.2% （15/17）,10.5% （2/17）,5.3% （1/17）,88.2% （15/17） for 5-year,and 82.3% （14/17）,15.8% （3/17）,10.5% （2/17）,82.3% （14/17） for 7-year. Conclusion Preoperative chemoradiation with capecitabine and SIB-IMRT is well tolerated and results in an encouraging pCR rate,anal sphincter operation rate,post-operative complications rate and OS,LRR,DMR,DFS for patients with locally advanced rectal cancer.