The inhibitory effects of diallyl sulfide (DAS) derived from allicin on in vitro and in vivo proliferation of human osteosarcoma MG-63 cells and the action mechanism, and the influence of DAS on invasive capability of MG-63 cells were investigated in order to search for the novel medicines for osteosarcoma. In the in vitro experiment, MG-63 cells were treated with different concentrations of DSA, and the morphological changes of MG-63 cells were observed under an inverted phase microscope. MTT method was used to assay the proliferation of MG-63 cells. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was used to detect the VEGF mRNA expression level in MG-63 cells. By using Transwell invasion assay, the influence of DAS on invasive ability of MG-63 cells was tested. In the in vivo experiment, the nude mice MG-63 cells tumor-bearing model was established, and different concentrations of DAS were injected beside the tumor. Twenty-one days after treatment, the mice were killed, the tumor size and tumor inhibition rate were calculated. The microvessel density (MVD) was determined by using immunohistochemistry. In the in vitro experiment, different concentrations of DAS could obviously inhibit proliferation of MG-63 cells in a time- and concentration-dependent manner. RT-PCR revealed that the expression levels of VEGF mRNA in DSA groups (different concentrations) were significant reduced as compared with those in control group (all P < 0.05). Transwell invasion assay indicated that in 20 and 40 mu g/mL DAS groups, the number of migratory cells was 91.4 +/- 8.3 and 81.8 +/- 7.4 respectively, which was significantly declined as compared with that in control group (150.4 +/- 14.7, both P < 0.05). In the in vivo experiment, DAS could significantly suppress the growth of MG-63 tumor-bearing tissue. Immunohistochemistry demonstrated that different concentrations (20 and 40 mu g/mL) of DAS could significantly decrease MVD of MG-63 tumor-bearing tissue (all P < 0.05). It was suggested that DAS could inhibit the growth of MG-63 cells probably by suppressing the expression of VEGF mRNA.