Ten isolates of Ralstonia solanacearum were isolated from naturally infected potato plants, collected from different localities of Gharbia, El- Minia, Assiut and sohag governorates. The isolate GK5 exhibited the highest wilt severity. Antibacterial activity of aqueous plant extracts of Hibsicus sabdariffa, Punica granatum and Eucalyptus, spp. were tested against Ralstonia solanacearum the causal pathogen of bacterial wilt of potato in vitro, vivo and field experiments. In vitro, all concentrations 25%,50%, 75% and 100% of the tested plant extracts were used against of the pathogen. Among all tested concentrations of plant extracts only the concentration 100% and 75% from extract Hibsicus sabdariffa found to be able to inhibit the growth of bacterial pathogen in vitro. In vivo experiment, all plant extracts tested significantly reduced diseases severity by Hibsicus sabdariffa (13.2%) followed by Punica granatum (35.85%). In field experiment, application of plant extracts caused highest reduction in severity of bacterial wilt. These three plant extracts showed the increased activity of defences related enzymes viz, peroxidase (PO), polyphenoloxidase (PPO) and phenylalanine ammonia- layes (PAL) in treated potato plants challenged with Ralstonia solanacearum. Significant activities of PO, PPO and PAL was observed at 8days after the treatment. The maximum PO (4.5 unit/ mg potein) treatment with Punica granatum.