Introduction Heavy ion radiotherapy has shown promising results in treating pelvic recurrence of rectal cancer. We report a case in which a patient underwent robot-assisted low anterior resection with transanal mesorectal excision (TaTME) following heavy ion radiotherapy, owing to challenges associated with spacer placement. Case presentation A 54-year-old man was diagnosed with upper rectal cancer. He underwent robot-assisted low anterior resection. Eight courses of CapeOX were administered as postoperative adjuvant chemotherapy. Immediately after completion of adjuvant chemotherapy (8 months postoperatively), computed tomography (CT) scan revealed a 30-mm large nodule on the dorsal surface of the oral anastomotic intestine, which was detected by positron emission tomography–CT. Given that the tumor had an indistinct border with the sacrum and its superior margin extended to the second sacrum, it was concluded that a combined sacral resection was not advisable, and heavy ion radiotherapy was indicated. Robot-assisted low anterior resection combined with TaTME was performed approximately 2 months after heavy particle radiotherapy [73.6 Gy (relative biological effectiveness)/16 sessions]. CT scan conducted 3 months after irradiation revealed substantial shrinkage of the recurrent tumor. Conclusion Robot-assisted resection of exposed colon with TaTME after heavy ion radiotherapy is regarded as an effective strategy for treating locally recurrent rectal cancer.