Identifying prognostic factors for osteosarcoma (OS) aids in the selection of patients who require more aggressive management. CD133 has been found to be a prognostic factor of certain tumor types. However, the association between CD133 expression and the prognosis of OS remains unknown. In this study, we analyzed the association of CD133 expression in OS with clinical factors and overall survival, and further investigated its potential role in metastasis in vitro. We found CD133 expression in 65.7% (46/70) of OS samples using immunohistochemistry, and it was positively correlated with lung metastasis analyzed by Chi-square test (P=0.002) and shorter overall survival time using the Kaplan-Meier method compared by log-rank test (P=0.000). Multivariate analysis showed that CD133 expression was an independent prognostic factor of patients with OS. To test for direct participation of CD133, we separated CD133(+) and CD133(-) cells in the MG63 cell line using magnetic-activated cell sorting and found that CD133(+) cells were more active in migration by scratch wound-healing assay and invasion by Matrigel invasion assay compared with CD133(-) cells. Elevated mRNA expression of the stemness gene octamer-binding transcription factor 4 (Oct-4) and NANOG, and the metastasis-related receptor C-X-C chemokine receptor type 4 (CXCR4) were also found in CD133(+) cells by reverse transcription-polymerase chain reaction. Thus, expression of CD133 was correlated with lung metastasis and poor prognosis in OS patients. CD133(+) cells may be a type of cancer stem cell with high expression of self-renewal capacity and metastasis-related genes.