Periprosthetic fracture following a proximal humeral intramedullary (IM) nailing is rarely reported neither for its occurrence nor for its treatment. Proximal humeral IM nail (Acumed, LLC, Hillsboro, OR, USA) has been increasingly reported of its successful treatment outcomes, yet there is paucity of data describing its complications. Here we report a 26 year-old female patient, who sustained a proximal humerus fracture which was initially successfully treated by proximal humeral IM nail, and was complicated by a periprosthetic fracture distal to the nail tip at postoperative 4 months. Serial application of U-shaped coaptation splint, hanging cast, and functional bracing resulted in satisfactory clinical outcome. Periprosthetic fracture after proximal humerus IM nail can occur by a low energy injury, which need to reminded in treating young and sports-active patients.