Aquaporins (AQP) are not only water channel protein, but also potential prognostic indicator and therapeutic target for rectal cancer. Some previous studies have demonstrated the AQP expression could be estimated by ADCaqp value derived from ultra-high b-value diffusion-weighted imaging (DWI). We aim to determine whether ADCaqp could be a new and specific biomarker for indicating the AQP expression and prognostic factors of rectal cancer. 76 untreated patients with rectal cancer confirmed by colonoscopy biopsy were enrolled. ADCaqp value was generated from ultra-high b-value DWI with five b-values (1700-3500 s/mm2). AQP (AQP1, 3 and 5)staining intensity was estimated by both of software (QuPath) and manual manner. The relationships between histogram features of ADCaqp and AQP staining intensity were analyzed. The correlations between histogram features of ADCaqp and differentiation degrees (good, moderate, poor), T stage (T1-2 vs T3-4), and lymph node status (N+ vs N-) were also evaluated respectively. The mean, 75th percentile and 97.5th percentile of ADCaqp were correlated with AQP1 staining intensity (r = 0.237, 0.323 and 0.362, respectively, all P < 0.05) . No correlation was found between the histogram features of ADCaqp and AQP3 or AQP5 staining intensity. The mean, 50th percentile, 75th percentile and 97.5th percentile of ADCaqp value exhibited significant differences between differentiation status (all P < 0.05). Histogram features of ADCaqp value showed no significant differences in two subgroups of T stage and lymph node status (all P > 0.05). Histogram analysis showed that the ADCaqp value derived from ultra-high b-value DWI of rectal cancer could reflect AQP1's expression and rectal cancer's malignancy degree. ADCaqp might be a new imaging biomarker for evaluating rectal cancer.