In this paper, the acute cytotoxicity of silver nanoparticles, as well as their influence on the adhesion state and membrane functions of Human Umbilical Vein Endothelial Cells ( HUVEC) and Human Umbilical Artery Smooth Musle Cells (HUASMC) were studied in vitro, for the sake of clinic using security. The results are as follows. Silver nanoparticles whose concentration ranged from 0.0039 mg/mL to 0.5 mg/mL did not show acute cytotoxicity within 8 hours, but the effects on the adhesion state of both cell lines were observed. The shape of the cells abnormally became small and round, which indicated that they were not well adhered on the culture plate. At the mean time, silver nanoparticles were found aggregating on the cell membrane, and the membrane fluidity and integrity of the cells were alternated, which implied that Ag nanoparticles had cytotoxicity in a certain degree.