Vascular endothelial growth factor (VEGF) is a specific mitogen of endothelial cells and plays an important role in vasculogenesis and angiogenesis. In recent years, both our and other laboratories have found that VEGF may be involved in embryo implantation. However, the relationship between VEGF and MMP-2 and MMP-9, the marker molecules of embryo implantation, is still unknown. In the present study, an examination of the effects of VEGF on the expression and secretion of MMP-2 and MMP-9 during implantation in mice was carried out by RT-PCR and gelatin zymography. The results show that VEGF antibody significantly decreased uterine mRNA levels of MMP-2 and MMP-9 during pregnancy, and that VEGF could up-regulate the activities of MMP-2 and MMP-9 secreted by blastocysts cultured in vitro in a time- and dose-dependent manner. The results suggest that, in the course of implantation, the ability for metastasis and invasion of blastocysts and the receptiveness of the uterus might be regulated by VEGF through its influence on the transcription and translation of MMPs.