Osteosarcoma (OS) is the most common primary malignant tumour of bone.Nearly30-40% of OS patients have a poor prognosis despite multimodal treatments.Because the carcinogenesis of OS remains unclear, the identification of new oncogenes that control the tumourigenesis and progression of OS is crucial for developing new therapies.Here, we found that the expression of Mediator of RNA polymerase Ⅱ transcription subunit 19 (Med19) was increased in OS samples from patients compared to normal bone tissues.