Primary chest wall tumors are rare and primary osteosarcoma of the chest wall is considered as an even rare among the primary chest wall malignant tumors. The main presentation is rapidly expanding painful mass with elevation of alkaline phosphatase. We present a case of a 34 years old male who was found to have an incidental asymptomatic large chest wall mass with normal alkaline phosphatase level. He underwent several radiological diagnostic modalities which showed the extent and delineation of the mass. Complete excision of the mass was achieved and the chest wall defect was reconstructed with Prolene mesh. The histopathology confirmed the diagnosis of osteosarcoma of the chest wall.