Aims To determine the biological correlation between apparent diffusion coefficient (ADC) values and Sirtuin1 (SIRT1) levels of tumour tissues in patients with esophageal carcinoma (EC), and to ascertain the treatment biomarker of ADC in predicting the early response of patients undergoing definitive chemoradiotherapy (CRT). Methods A total of 66 patients were enrolled, and the specimens of tumour tissues were collected before treatment to perform immunohistochemical (IHC) examinations and quantify the levels of SIRT1. Then all patients were given two esophageal magnetic resonance imaging (MRI) examinations with diffused weighed imaging (DWI) including pretreatment and intra-treatment (1 similar to 2 weeks after the start of radiotherapy). The regions of interest (ROIs) were contoured according to the stipulated rules in advance using off-line software, and the values of the ADC in the ROIs were generated automatically. Then, the values of the ADC at baseline and intra-treatment were labeled as pre-ADC and intra-ADC respectively, and Delta ADC, ADC(ratio) were calculated. Pearson's correlation coefficients were acquired to estimate the correlation between each of ADC values and SIRT1 levels. Spearman's rank correlation coefficients were acquired to estimate the correlation between early response and the values of each ADC. Receptor operation characteristics (ROC) curves were constructed to estimate the accuracy of the ADC in predicting the early response of CRT. Results The findings of this study showed different correlations between ADC values and the levels of SIRT1 (Delta ADC: r = - 0.943, P = 0.002; ADC(ratio): r = - 0.911, P = 0.000; intra-ADC: r = - 0.748, P = 0.002; pre-ADC: r = 0.109, P = 0.558). There was a positive correlation between Delta ADC and early response to treatment (rho = 0.615, P = 0.023), and multivariable logistic regression revealed that Delta ADC was significantly associated with short-term response of CRT in esophageal carcinoma patients. Conclusions In summary, early increases in ADC may facilitate the predication of early CRT response in patients with esophageal squamous cell carcinoma (ESCC), which may be attributed to the different correlation between ADC changes and SIRT1 expression.