Postmastectomy nipple necrosis is a factor that leads to a poor aesthetic outcome in breast reconstruction because of the unique projective structure of the nipple. We present a case of successful nipple reconstruction using a de-epithelialized rectangular flap. A 45-year-old woman was diagnosed with left breast cancer. She had a vertical scar below the nipple-areolar complex due to previous reduction mammoplasty. She underwent nipple-sparing mastectomy, breast reconstruction with a deep inferior epigastric artery perforator (DIEP) flap, and contralateral reduction. After the operation, the nipple gradually necrotized, and full-thickness nipple necrosis was observed on postoperative day 12. For nipple reconstruction, we designed a 38×23 mm rectangular flap from the DIEP flap considering the contralateral nipple diameter (12 mm), protrusion (2 mm), and ipsilateral mastectomy skin flap thickness (15 mm). The area in contact with the mastectomy skin flap was placed in the defect area after de-epithelialization. The reconstruction was successful and the nipple survived with a slight loss of projection. When unexpected nipple necrosis occurs after DIEP-based breast reconstruction, designing a de-epithelialized rectangular flap using the DIEP flap tissue is a feasible reconstructive method to consider.