Although ubiquitination of DX2, novel oncogene, is significant on its protein stability, but DX2 ubiquitination sites are not unveiled. In this study, we identified ubiquitination sites of DX2 upon treatment with DX2 protein inhibitor, SDL01, via LC-MSMS technique. Lysine 90 of DX2 was revealed as a ubiquitination site and was validated as a real ubiquitination site via molecular biology