Purpose To investigate the potential of texture analysis applied on T2‐w and postcontrast T1‐w images acquired before radiotherapy for prostate cancer (PCa) and 12 months after its completion in quantitatively characterizing local radiation effect on the muscular component of internal obturators, as organs potentially involved in urinary toxicity. Methods T2‐w and postcontrast T1‐w MR images were acquired at 1.5 T before treatment (MRI1) and at 12 months of follow‐up (MRI2) in 13 patients treated with radiotherapy for PCa. Right and left internal obturator muscle contours were manually delineated upon MRI1 and then automatically propagated on MRI2 by an elastic registration method. Planning CT images were coregistered to both MRIs and dose maps were deformed accordingly. A high‐dose region receiving >55 Gy and a low‐dose region receiving <55 Gy were identified in each muscle volume. Eighteen textural features were extracted from each region of interest and differences between MRI1 and MRI2 were evaluated. Results A signal increase was highlighted in both T2‐w and T1‐w images in the portion of the obturators near the prostate, i.e., in the region receiving medium‐high doses. A change in the spatial organization was identified, as an increase in homogeneity and a decrease in contrast and complexity, compatible with an inflammatory status. In particular, the region receiving medium‐high doses presented more significant or, at least, stronger differences. Conclusions Texture analysis applied on T1‐w and T2‐w MR images has demonstrated its ability in quantitative evaluating radiation‐induced changes in obturator muscles after PCa radiotherapy.