melissa officinalis  is a well known medisinal plant.different studies performed in mice have shown the sedative.hyonotic,analgesic,antiviral amd antimicrobial effects of this plant.the present  investigation was undertaken to evaluate the effect of percolated extract of this plant against lethal seizure induced by intraperitional injection of pentylentetrazole (PTZ) in wister rats.the study was performed on three groups of animals pretreared with difeerent dose of extract via  intraperitional injection.after 30 minutes each animal received high  dose of PTZ (90mg/kg) for induction of lethal seizure.the control group received normal saline.in addition a positive control group pretreated with diazepam,a well known drug in the treatment of seizure,was used for comparison.the efficacy of the extract to protect the animals adainst lethal seizure was based on the latency of the arrearance of the first sing of seizure or the latency of the different epileptic manifestations and decrease of mortality rate in each group.the results showed that various cpileptic manifestation are delayed in diazepam pretreated animals and exdtract compared with control group.the dose of 50mg/kg of the extract appeared ti be significantly effective on the tremores and the myoclonic jerks of epileptic manifestations(p<0.05).in addition the mortality rate was significantly reduced in pretreated animals with this dose compared with control group(p<0.05)mortality rate was 88%in saline group,13%in 50mg group and zero percent in diazepam group.the results indicated that the extract of mellisa officinalis possesses anticonvulsant property.