Osteochondral avulsion fracture of patella has been rarely reported. We experienced one case of osteochondral avulsion fracture which was developed after abscess around knee. The patient was a 16year old with the history of abscess. The presenting symptom was knee pain and loss of extension power. Radiologic and operative findings suggested that osteochondral avulsion fracture of the patella, was caused by minor trauma near the insertion site of quadriceps tendon. In usual case of quadriceps tendon rupture, the rupture occurred at the musculotendinous junction, caused by sudden contracture of the muscle without trauma history. This case was treated successfully with tension band wiring technique. Differential diagnosis between osteochondral avulsion fracture and osteomyelitis of patella was emphasized.