Respiratory failure is the most serious manifestation and usual cause of death in acute organophosphate poisoning, and is common in acute cholinergic crisis. But the respiratory failure may appear suddenly in a patient who is recovering from the cholinergic crisis, even while receiving conventional therapy. These are case report of 37 years old male and 24 years old female with intermediate syndrome in organophosphate poisoning. The two patients ingested organophosphate(fenthion and mixture of DDVP with chlorpyrifos respectively) incidentally and in a sucide attempt respectively. After apparent recovery from the cholinergic crisis with a conventional therapy but before the expected onset of delayed polyneuropathy, the respiratory failure appeared suddenly with a muscular weakness, affecting predominantly the proximal limb muscles, neck flexors, territories of several motor cranial nerves. The two patients needed mechanical ventilatory support and recovery from the intermediate syndrome was complete in both patients, although one subsequently developed hypoxic encephalopathy. The clinical manifestation and electrophysiologic study support the clinical diagnosis of intermediate syndrome. The syndrome carries a risk of death. because of respiratory paralysis, if not recognized early and treated adequatedly. Prompt endotrachial intubation and mechanical ventilatory support is the cornerstone of treatment of the intermediate syndrome. Therefore, all patient should be observed in a hospital for up to 5 days after poisoning.