Ewing’s sarcoma (ES) is a highly aggressive bone tumor, and the second most prevalent pediatric bone malignancy. The presence of metastasis at diagnosis decreases the three-year survival rate to 20% and contributes to diminished prognosis. Researches are indispensable for the early characterization of the disease and prediction of metastatic-prone patients, through biomarkers identification. Moreover, there is currently no available data on ES utilizing non-biopsy samples, such as plasma. This study utilizes a proteomic analysis of Ewing's sarcoma patient’s plasma samples and biopsies. Initially, the ES group was compared with the control counterpart. In a next step, the ES arm was further stratified into either initially metastatic and non-metastatic, or poor and good chemotherapy responder groups to identify protein expression profiles that can predict metastatic proneness and chemotherapy response, respectively.