Vasodilator-stimulated phosphoprotein regulates osteosarcoma cell migration. Vasodilator-stimulated phosphoprotein (VASP) has been reported to play an important role in the process of cell migration and tumor metastasis. However, to date, no study has examined VASP expression and its function in osteocarcoma cells. In this study, we analyzed the effect of VASP on osteosarcoma cell migration and the signal transduction pathways involved. We used two osteosarcoma cell strains (Mg-63 and Saos-2 cells) with different metastatic potential. Silencing of VASP gene expression was carried out using RNA interference in these cells. Knockdown of expression at the transcriptional or translational level was determined by RT-PCR or western blot analysis, respectively. The metastatic potential of the tumor cells was determined by a wound healing migration assay. VASP mRNA expression was also determined in 30 human osteosarcoma samples. Furthermore, Rac1 was determined as a regulator of VASP function. RT-PCR and western blotting showed that Mg-63 cells had a significantly higher VASP expression at both the transcriptional and translational levels compared to Saos-2 cells. The wound healing assay revealed that Mg-63 cells had more migratory potential compared to Saos-2 cells. The effect was found to be reversible when VASP was knocked down by siRNA in Mg-63 cells. Specimens from human patients with metastases had higher VASP expression compared to specimens of patients without metastases. Knockdown of Rac1 resulted in inhibition of VASP expression in sarcoma cells. These results suggest that VASP protein regulates osteosarcoma cell migration and metastasis. Rac1 and VASP interaction may be a potential target for osteo-sarcoma treatment.