Abstract: Objective To evaluate the effect and toxicity of postoperative three-dimensional conformal/intensity modulated radiotherapy combined with chemotherapy and chemotherapy alone on locally advanced rectal carcinoma. Methods A total of 226 patients with locally advanced rectal carcinoma who had undergone radical mesorectal excision were retrospectively analyzed, including 116 patients with postoperative adjuvant chemotherapy (Group A) and 110 patients with adjuvant chemoradiotherapy (Group B). All chemotherapy were from 2 cycles to 8 cycles, a median of 4 cycles. There were 88 patients who had been treated by three-dimensional conformal radiotherapy and 22 patients were treated by intensity modulated radiotherapy. A median dose of radiation was 50 Gy (45-54) Gy. The toxicity, local recurrent rates, overall survival rates, and disease-free survival rates between the two groups were analyzed statistically. Results 1-, 2-, 3-year local recurrent rates were 15.5%,29.7%,33.2% in Group A and 3.8%, 10.5%, 10.5% in Group B (P=0.001).1-,2-,3-year overall survival rates were 95.6%,68.4%,53.5% in Group A and 94.2%,76%,70.7% in Group B.The differences between two groups were close to statistical significance (P=0.059). 1-, 2-, 3-year disease-free survival rates in two groups were not statistically signifi cant (P=0.608). The incidence of gastrointestinal and hematological toxicity were higher in Group B than those in Group A（78.2% vs. 41.4%, P=0.000; and 64.5% vs. 30.2%, P=0.000）. The differences of 1-, 2-, 3-year overall survival rates and disease-free survival rates were not statistically signifi cant between Group B and Group A in stage Ⅱ patients (P=0.810 and P=0.067）. 1-, 2-, 3-year overall survival rates in Group B was higher than those in Group A in stage Ⅲ patients (P=0.047). As for disease-free survival rates, there were no signifi cant difference between two Groups (P=0.201). Radiation enteritis occurred in 20.9% of patients and radiocystitis occurred in 10% patients in Group B. No patient got toxicity in grade Ⅲ and more. Conclusion Postoperative threedimensional conformal/ intensity modulated radiotherapy combined with chemotherapy could decrease local recurrent rate obviously, and increase overall survival rate for locally advanced rectal carcinoma patients in stage Ⅲ. Hematological and gastrointestinal toxicity in adjuvant chemoradiotherapy group was higher than those in chemotherapy alone group, but all patients could tolerate the treatment well. Compared with conventional radiotheraphy, three-dimensional conformal/ IMRT could decrease the incidence of radiocystitis and radiation enteritis.