We report two cases of prostatic cancer invading the rectum with circumferential rectal wall thickening. In both cases, reddish and uneven edematous mucosa was observed by colonoscopy and the boundary of the lesion was indistinct. No mass or ulcer formation was not observed. CT scan showed irregular prostatic swelling and circumferential rectal wall thickening adjacent to the prostate. The rectal biopsy specimen showed moderately to poorly differentiated adenocarcinoma, and it was positive on PSA immunostaining. Although rectal invasion of prostatic cancer is relatively rare, it is important to be aware that prostatic cancer can cause circumferential stenosis of the rectum.