A 12-year-old boy suffered a head injury and lost his iPhone 4 when he was robbed at knifepoint.
The boy was attacked by four teenagers off Donnington Bridge.
He was later taken to the John Radcliffe Hospital and treated for a head injury.
The crime happened in Meadow Lane at 7.45pm on March 19 but police have only released the details today.
Police described the robbers as Asian and aged between 15 and 17 years old.
A 17-year-old was arrested on suspicion of robbery on March 19 and bailed until April 22.
Anyone with information about the attack can call the Oxford Mail on 01865 425427