Abstract: Two tobacco cultivars differing in resistance to P solanacearum were used in this study． Effects of P solanacearum infection on leaf hydrogen peroxide(H₂0₂)metabolism and chlorophyll fluorescence were studied．Contents of H₂0₂ and ma1ondia1dehyde(MDA)，production rate of superoxide radical(0₂^-)in plants infected with P solanacearum increa sed and the extent of increa se was significantly less in resistant cultivar than in susceptible one．Superoxide dismutase(SOD)activity decreased after the early stage of infection，then increased；SOD activity of resistant cultivar was higher than that of susceptible one．Catalase(CAT)activity increased at the early stage of infection，then decreased．The extent of decrease in CAT activity was greater in susceptible cultivar than in resistant one．Peroxidase(POD)activity decreased at the early stage of infection，then increased．The extent of increase in POD activity was higher in susceptible cultivar than in resistant one．The variable fluorescence of chloroplasts(Fv)，the efficiency of primay conversion of light energy of PS II(Fv／Fm)and potential activity of PS II(Fv／Fo)of plants infected P solanacearum decreased，the extent of decrease was higher in susceptible cultivar than in resistant one． Above-mentioned results suggest that the res istance of tobacco to P solanacearum is highly related to H₂0₂ metabolism and parameters of chlorophyll fluorescence．