Osteochondroma is the most common benign bone tumor around the metaphysis. Usually, it is originated from the peripheral area of metaphysis-physis junction due to mutation of physeal chondrocyte. This 1-year and 3-month-old boy presented with a mallet deformity. Radiographs showed an abnormal mass on the distal part of the middle phalanx. It was connected to the articular cartilage which was not associated with the physis. Operative and pathologic findings showed typical osteochondroma. After excision of the osteochondroma with sparing of the extensor tendon and immobilization for 6 weeks with a full extension splint, the pseudomallet deformity disappeared.