Abstract: Nanometer TiO2 photosemiconductor, as a safe antibacterial chemical with a long-effect, has been widely applied to medicine and environmental protection. The authors studied the effects of TiO2 sol on plant pathogens. Nano-TiO2 semiconductor sol was prepared referring to the method developed by Itinose, by which a successive and transparent antibacterial membrane was formed on aseptic tiles, Wood's lamp radiation, statistics antibacterial ratios, to detect antibacterial effectiveness. The results show that the nano-TiO2 was anatase, and mean diameter was 30.6 nm, dispersity, stability and adhesive power were good. The antibacterial experiments show that the effect of the three antibacterial membranes is the best; when the antibacterial membrane is above three, it is easy exfoliated; compared with the blank, nano-TiO2 semiconductor sol has excellent antibacterial effect on plant pathogens, and as the time lasts, the antibacterial rate increases. The results of relative antibacterial rate show that when the illumination lasts for 24 h, the relative antibacterial rate reaches 100%, and there is no discrepancy for different strains. So nano-TiO2 semiconductors sol is a potent and broad spectrum antibacterial.