The anticonvulsive, sedative and hypothermic effects of water and ethanol extracts of Periostracum Cicadae (PC), the cast off skin of Cryptotympana atrata were studied. The water-extract of whole Periostracum Cicadae (PCws) had anticonvulsive, sedative and hypothermic effects in rats. Orally, it decreased carrageenin-induced hyperthermia. The hypothermic effect of PCws was potentiated by 5-hydroxytryptophan and antagonized by p-chlorophenylalanine. PCws enhanced the decrease in locomotor activity induced by alpha-methyl-p-tyrosine or 5-hydroxytryptophan and reduced the increase in locomotor activity produced by levodopa plus benserazide or p-chlorophenylalanine. From these results, it was concluded that the sedative and hypothermic effect of PCws may be due to an increase in central serotonergic activity.