Chest wall resections and reconstructions are routinely performed to close defects after primary breast tumor resections. Depending on the size of primary breast tumors, the reconstructive technique requires more challenging approaches. In this study, we would like to introduce a novel technique which can be applied as a method in covering various sizes of skin defects after mastectomy termed as “horse-shoe flap technique.” We conducted a series of case reports of patients who underwent chest wall coverage after primary breast tumor resections between October 2018 and November 2019 and selected five cases of breast cancer patients. These patients were treated with the horse-shoe flap technique which relies on shape as its main concept. All chest defects must form a circular shape, based on the principle that adequate safe tumor margins are best achieved with a circular incision. The donor flap was drawn and taken from the outer circle area with a larger arc, depending on the defect's diameter size. Five post-mastectomy chest wall defect cases had been successfully closed with this technique. Patients were all female, ranging from 36 to 55 years of age. The smallest chest defect was 4 cm in diameter, and the largest was 26 cm. All the defects were closed using a 120-degree horse-shoe flap design. One patient experienced marginal necrotic skin, and one case had formed postoperative seroma. The horse-shoe flap technique proves to be an excellent option for closing chest skin defects which can be applied for various sizes of skin defects with minor complications.