Aim: Gracilis autograft repair for an isolated atraumatic peroneus brevis rupture. Background: Peroneal tendon injuries are one of the causes of lateral ankle pain and instability that can either involve peroneus brevis tendon (PBT) or peroneus longus tendon (PLT). PBT tears are often associated with trauma, leading to forced dorsiflexion of ankle or chronic subluxation. Atraumatic tear of PBT is rare, with only a few cases described. The surgical management for PBT tear includes peroneal tendoscopy, debridement and tubulization of remaining tendon and tenodesis. There is no consensus regarding the optimal surgical intervention for irreparable tears. Case description: A 43-year-old businessman presented to our clinic with complaints of pain and swelling in lateral side of left ankle of 1 week duration. The clinical examination revealed high-arched foot with diffuse swelling over the retrofibular area with tenderness elicited along the line of PBT. The sagittal view of ankle MRI showed completed tear of PBT. A curvilinear lateral incision was made along the posterior border of fibula. The proximal end of donor graft was secured to the proximal end of remaining PBT using pulverate weaving technique, while the distal end graft was looped through the drill hole in 5th metatarsal base and sutured to itself. Conclusion: Autograft is biologically superior to allograft with the advantages of tissue compatibility and faster reincorporation. Clinical significance: Surgical management of PBT tears are advocated for active, symptomatic, or patients who fail to improve with conservative management.