Abstract : Colorectal cancer (CRC) is a serious health condition. surgery is the cornerstone of curative therapy for early-stage rectal cancer, neoadjuvant chemoradiation (NCRT) has emerged as a standard treatment option for locally advanced rectal cancer (LARC). The acute toxicity from NCRT remains a limiting factor for treatment compliance and quality of life in patients with LARC. To evaluate the acute GI toxicity profiles of locally advanced carcinoma rectum patients receiving 3DCRT versus IMRT. During this hospital-based prospective randomised observational study, patients with carcinoma rectum were enrolled between September 2018 and December 2020 at Acharya Harihar Post Graduate Institute of Cancer, Cuttack. A total of 54 patients with locally advanced carcinoma rectum were included, among whom 30 patients were treated by 3DCRT (Arm A) and another 24 patients were treated by IMRT (Arm B) with daily concurrent Capecitabine. Out of 15 patients in the 3DCRT arm, eight had grade 2 diarrhea. Six patients had grade 3 diarrhoea during the 5th week of radiation and had to be admitted to the hospital for supportive care. In the IMRT arm, 2 out of 12 patients had grade 2 diarrhea. There was a significant difference between the various groups in terms of the distribution of diarrhoea grade 2 (χ2 = 0.127, p = 0.043). Greater conformity can be achieved with IMRT by optimally modulating the intensity of individual beams, reducing doses to organs at risk and thus decreasing the rate of gastrointestinal toxicity. The use of IMRT for rectal cancer may also potentially prevent surgery delays, improve postoperative healing, and allow for better adjuvant chemotherapy tolerability.