Delirium may present with hyperactive, hypoactive or mixed clinical pictures. The signs of hypoactive delirium are lethargy, confusion, apathy, hypersomnia, muttering, difficulty in maintaining attention, and difficulty in understanding and performing commands. Valproate is commonly used for the treatment of epilepsy and bipolar disorders. It is also used for the management of alcohol withdrawal delirium and agitative-aggressive deliriums. However, few reports are available about the valproate-induced delirium. In this report, we present a 46 years-old woman with bipolar disorder for 14 years. During her last two hospital admissions, she had been diagnosed with manic episode with psychotic features and she had received valproate. She experienced three hypoactive delirium episodes lasting 2-3 days throughout the treatment period of first week. The patient predominantly had the following signs; vomiting, hypersalivation, confusion, drowsiness, dysphasia, and hypoactivity. At the first day of delirium episode, serum valproate level was found to be within the therapeutic range (98.4, 117.1, and 65.6 μg/ml; respectively). In addition, she had normal results of cranial MRI, complete blood count, urine analysis, electrocardiogram, ALT, AST, albumin, bilirubin, BUN, creatinine and electrolytes. The serum ammonia level of the patient could not been measured due to limitations of laboratory facilities. The patient?s consciousness improved dramatically 2-3 days after cessation of valproate.In conclusion, valproate can induce delirium at therapeutic blood levels in some patients via various mechanisms and this side effect has to be considered during valproate use.