Abstract: Inhibitory effects of ozone solution on spore germination of Phytophthora infestans (Mont.) de Bary were tested and the morphological change of sporangia was observed under microscope. The results showed that spore germination rate was closely related to ozone concentrations. More than 95% spores were inhibited at concentration of 9 mg/Kg and 100% spores were restrained at 18 mg/Kg. While the treating time 1 minute and 2 minutes had no significant difference at both concentrations. Morphological deformation was found after 72 hours treated with high concentration of ozone solution. As ozone solution at high concentration has no toxicity to plants, it showed much potential to be used in controlling late blight in field.