Objective To study the effect of MMP-9 over-expression on invasion and migration of osteosarcoma 143B cells. Methods Lentivirus-mediated MMP-9 over-expression vector was transfected into osteosarcoma 143B cells. The experiment was divided into an experimental group (transfected with pLV-Puro MMP-9 over-expression sequence), a control group (transfected with pLV-Puro MMP-9-NC sequence) and a blank group (PBS). qRT-PCR was used to detect the expressions of MMP-9 and VEGF mRNAs. The expressions of MMP-9 and VEGF proteins were detected by Western blot. Transwell invasion assay was used to detect the invasion ability. Cell migration was measured by cell scratch test. Results The mRNA and protein expressions of MMP-9 and VEGF in the experimental group were significantly higher than those in the control and blank groups (P < 0.05). The number of cells passing through the artificial basement membrane in the experimental group was significantly larger than that in the control group and the blank group (P < 0.05). The healing rate of scratches in the experimental group was significantly higher than that in the control group and the blank group (P < 0.05). Conclusions Lentivirus-mediated MMP-9 overexpression inhibits the invasion and migration of osteosarcoma 143B cells by acting on VEGF target gene.