Response to neoadjuvant therapy (NAT) in patients with locally advanced rectal cancer (LARC) has a great impact on further management strategy. MRI and FDG- PET/CT using RECIST and PERCIST response criteria respectively play an important role in response assessment. Aim: To detect the value of MRI and PET/CT using RCIST and PERECIST criteria in assessment of response to NAT in patients with LARC with comparison between diagnostic performance of both diagnostic modalities. Patients and methods: A total of 30 patients with LARC were included, PET/CT and Pelvic MRI were performed pre and post NAT followed by surgical resection. Imaging studies were analyzed and response was evaluated with RCIST and PERECIST response criteria and subsequently correlated with post-operative pathological results. Results: Assessment response criteria for MRI (RECIST) and for PET/CT (PERCIST) showed statistically significant correlation with pathological response. Discordance response results between both studies were found in 7 patients (23.3%). MRI using RECIST response criteria has better specificity (78.3 % vs 47.8 %), positive predictive value (58.3 %vs 36.8%) and overall accuracy (83.3% vs 60%) in comparison to PET/CT using PERCIST response criteria. Conclusion: MRI and PET/CT using RECIST and PERCIST response criteria have significant value for assessment of response to NAT in patients with LARC with relatively more superior diagnostic performance figures for the former.