Twenty-three patients with esophageal squamous cell carcinoma (ESCC) underwent intravoxel incoherent motion (IVIM) MRI at four timepoints: pre, mid, end, and post-CRT to assess the value of IVIM parameters in the early assessment of treatment response to CRT. The parameters and their change percentages were compared between complete response (CR) and partial response (PR). ADC, f, %ADC, and %D at mid-CRT in CR group were significantly higher than those in the PR group. D combined with f and ADC had highest area under curve in identifying CR from PR. IVIM parameters proved useful in assessing response to definitive concurrent CRT.