Objective To develop and validate a Union Model integrating clinical features with radiomics signatures derived from intratumoral and peritumoral T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) for the non-invasive prediction of p53 expression in intrahepatic mass-forming cholangiocarcinoma (IMCC).Furthermore, the study aims to determine the optimal predictive range.Methods This retrospective study included IMCC patients with immunohistochemically confirmed p53 expression status from four institutions. Patients were allocated into training, internal validation, and external validation cohorts. Multi-scale regions of interest, integrating the intratumoral volume with peritumoral expansions of 0, 3, 5, 10, 15, and 20 mm, were delineated on the MRI sequences. Radiomics and clinical features were extracted to construct single-sequence intratumoral and peritumoral models, a Fusion Model, a Clinical Model, and a Union Model. Performance was assessed using receiver operating characteristic (ROC) curves, area under the curve (AUC), accuracy, sensitivity, and specificity. Model interpretability was explored via SHapley Additive exPlanations (SHAP) values.Results The intratumoral and peritumoral 5mm models based on DWI and T2WI sequences demonstrated robust performance, yielding AUCs of 0.959 and 0.987 in the training cohort, and 0.821 and 0.809 in the internal validation cohort, respectively. The Union Model demonstrated the best predictive performance, with AUC values of 0.992, 0.945, and 0.825 across the three cohorts.Conclusion A multimodal Union Model incorporating intratumoral and 5-mm peritumoral MRI features can effectively predict p53 expression in IMCC, demonstrating favorable generalizability and potential for clinical decision-making.