Objective: The aim of the study was to compare the difference of dose distribution in clinical target volume and organ at risk (OAR) between five-field intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3DCRT) in the radiotherapy of rectal cancer. Methods: Fifteen patients with rectal cancer treated with radiotherapy (RT) were retrospectively analyzed. Among the patients, seven received RT preoperatively and 8 postoperatively. The target volume and the OARs such as the small bowel, bladder and femoral heads were contoured for each patient. 3DCRT-plan and IMRT-plan were performed for each patient respectively, with the prescribed dose covering at least 95% of the planning target volume (PTV). The conformity index (CI) and homogeneity index (HI) were used for evaluation of the dose distribution in the target volume, and the Dx% (the lowest dose to the x% volume of the OARs that received the highest dose of irradiation) and the mean dose were used for evaluation of the dose to OARs. Paired-T test was used for comparison of the difference between the two plans. Results: In the IMRT-plan and 3DCRT-plan, the CI were 0.94 and 0.87 (P = 0.000) and the HI were 1.13 and 1.17, respectively (P = 0.001). For small bowel, the D30%, D50% and the mean dose were 19.67 Gy, 15.13 Gy and 18.81 Gy in the IMRT-plan and 25.20 Gy, 22.20 Gy and 22.89 Gy in the 3DCRT-plan, respectively (P < 0.001 for all pairs of parameters). For bladder, the D30%, D50%, and the mean dose were 24.80 Gy, 34.20 Gy and 28.70 Gy in the IMRTplan, and 35.07 Gy, 44.67 Gy and 35.68 Gy in the 3DCRT-plan, respectively (P < 0.001 for all pairs of parameters). For femoral heads, the D5% in the IMRT-plan and 3DCRT-plan were 40.6 Gy and 40.47 Gy, respectively (P = 0.936), and the mean dose were 30.14 Gy and 25.57 Gy, respectively (P = 0.001). Conclusion: Five-field IMRT-plan is better than 3DCRT-plan in the conformity and the dose homogeneity within target volume and also better in sparing the small bowel and bladder. Objective: The aim of the study was to compare the difference of dose distribution in clinical target volume and organ at risk (OAR) between five-field intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3DCRT) in the radiotherapy of the patients, seven of the received RT preoperatively and 8 postoperatively. The target volume and the OARs such as the small bowel, bladder and femoral heads were contoured for each patient. 3DCRT-plan and IMRT-plan were performed for each patient respectively with the prescribed dose covering at least 95% of the planning target volume (PTV). The conformity index (CI) and homogeneity index used for evaluation of the dose distribution in the target volume, and the Dx% (the lowest dose to the x% volume of the OARs that received the highest dose of irradiation) and the mean dose wer Paired-T test was used for comparison of the difference between the two plans. Results: In the IMRT-plan and 3DCRT-plan, the CI were 0.94 and 0.87 (P = 0.000) and For Small bowel, the D30%, D50%, and the mean dose were 19.67 Gy, 15.13 Gy and 18.81 Gy in the IMRT-plan and 25.20 Gy, 22.20 Gy and 22.89 (P = 0.001) For bladder, the D30%, D50%, and the mean dose were 24.80 Gy, 34.20 Gy and 28.70 Gy in the IMRT plan, and 35.07 Gy, respectively. 44.67 Gy and 35.68 Gy in the 3DCRT-plan, respectively (P <0.001 for all pairs of parameters). For femoral heads, the D5% in the IMRT-plan and 3DCRT-plan were 40.6 Gy and 40.47 Gy, respectively (P = 0.936), and the mean dose were 30.14 Gy and 25.57 Gy, respectively (P = 0.001). Conclusion: Five-field IMRT-plan is better than 3DCRT-plan in the conformity and the dose homogeneity within target volume and also better in sparing the small bowel and bladder