Objective: This study was done to compare between the effect of preoperative radiotherapy and postoperative radiotherapy in treatment of resectable rectal carcinoma. The primary endpoints are local recurrence rate, overall survival (OS) and disease free survival (DFS). The secondary endpoints are to evaluate down-staging, treatment toxicity, and ability to do sphincter preservation, aiming at choosing the optimal treatment modality. Methods: This study included 100 patients with resectable rectal carcinoma who presented to Surgical Gastro Entrology Center and Clinical Oncology and Nuclear Medicine Department, Mansoura University during the period between January 2007 and September 2009. The included patients were randomized in two groups; group I: 50 patients received preoperative radiotherapy and group II: 50 patients received postoperative radiotherapy. Concurrent 5-fluorouracil-based chemotherapy was given to all patients. Two major types of surgery were done: abdomino-perineal resection with a permanent colostomy and low anterior resection with colorectal or coloanal anastomosis. Results: Preoperative radiotherapy resulted in pathologic complete response in 3 patients. T down-staging occurred in 18 out of 50 patients (36%) with statistically significant difference (P = 0.008). N down-staging occurred in 10 out of 24 patients. Sphincter preservation was more in group I. Delayed wound healing was the most common postoperative complication in group I with no significant difference. After a median follow up of 18 months, local recurrence rate and distant metastasis were higher in group II. The 2-year disease free survival was 72% and 60% in group I and II respectively with no statistically significant difference between both groups. Conclusion: This study concluded that preoperative radiotherapy is better than postoperative radiotherapy as regard local control, sphincter preservation with higher disease free survival and overall survival. No difference in treatment toxicity between both groups. Objective: This study was done to compare between the effect of preoperative radiotherapy and postoperative radiotherapy in treatment of resectable rectal carcinoma. The primary endpoints are local recurrence rate, overall survival (OS) and disease free survival (DFS). The secondary endpoints are to Evaluate down-staging, treatment toxicity, and ability to do sphincter preservation, aiming at choosing the optimal treatment modality. Methods: This study included 100 patients with resectable rectal carcinoma who presented to Surgical Gastro Entroology Center and Clinical Oncology and Nuclear Medicine Department, Mansoura University during the period between January 2007 and September 2009. The included patients were randomized in two groups; group I: 50 patients received preoperative radiotherapy and group II: 50 patients received postoperative radiotherapy. Concurrent 5-fluorouracil-based chemotherapy was given to all patients Two major types of surgery were done: abdomino-perineal rese Results: Preoperative radiotherapy resulted in pathologic complete response in 3 patients. T down-staging occurred in 18 out of 50 patients (36%) with phasic complete difference (P = 0.008). N down-staging occurred in 10 out of 24 patients. Sphincter preservation was more in group I. Delayed wound healing was the most common postoperative complication in group I with no significant difference. After a median follow up of 18 months, local Recurrence rate and distant metastasis were higher in group II. The 2-year disease free survival was 72% and 60% in group I and II respectively with no negative ly significant difference between both groups. Conclusion: This study concluded that preoperative radiotherapy is better than Postoperative radiotherapy as regard local control, sphincter preservation with higher disease free survival and overall survival. No difference in treatmentToxicity between both groups.