Purpose <p>To determine whether the apparent diffusion coefficient (ADC) parameters of tumor and distal paracancerous tissues in rectal adenocarcinoma (RA) derived from diffusion weighted imaging (DWI) can be associated with the tumor stages.</p> Materials and methods <p>134 consecutive patients with RA underwent preoperative DWI. ADC values of the tumor, distal tumor-adjacent and tumor-distant tissues were measured (recorded as ADC_t, ADC_dta and ADC_dtd, respectively). Additionally, ratios of ADC_t to ADC_dta (ADC_t/dta), ADC_t to ADC_dtd (ADC_t/dtd), and ADC_dta to ADC_dtd (ADC_dta/dtd) were calculated. Student’s t-test or Mann–Whitney U test, with false discovery rate (FDR) correction, was performed to compare the differences in the aforementioned ADC parameters between different tumor stages. The diagnostic efficacy of individual ADC and combined ADC parameters was evaluated using logistic regression analysis and receiver operating characteristic (ROC) analysis to predict tumor stages.</p> Results <p>Tumors with pT_3–4 stage demonstrated significantly lower values of ADC_t, ADC_t/dta, and ADC_t/dtd compared to those with pT_1–2 stage; tumors with pN_1–2 stage exhibited significantly lower values of ADC_t and ADC_t/dta compared to those with pN₀ stage; and cases with lymph node metastasis (LNM) showed significantly lower values of ADC_t, ADC_t/dta, and ADC_t/dtd compared to those without LNM (all FDR- corrected <i>P</i>-values &lt; 0.10). Area under the ROC curves (AUC) of the combination involving ADC_t and ADC_t/dta was higher than that of individual ADC parameters when assessing pT stage, pN stage, and LNM.</p> Conclusion <p>The ADC parameters of tumor and distal paracancerous tissues may provide supplementary information for preoperatively assessing tumor stages in RA.</p>