Cerastes cerastes cerastes is an Egyptian viper which belongs to the family of Viperidae and the genus Cerastes. There is no available information on the neurotoxic action of C.c.cerastes. The present work aimed to test the neurotoxicity of Cerastes cerastes cerastes crude venom and to isolate and purify the neurotoxic fraction(s). The neurotoxicity was verified by neuromuscular techniques (rat phrenic nerve hemi diaphragm, RPNH), and neurobehavioral experiments. The present results showed that Cerastes venom (20 µg/ml) and a purified caseinolytic fraction (10 µg/ml) inhibited the contractile responses of indirect RPNH. The contractile responses to acetylcholine (10^-3 M), carbachol (2x10^-6 M) and KCl (60 mM) were inhibited by the venom and the purified fraction. However, i.p. injection of the fraction (73 µg/100gm b.w) elicited a group of behavioral changes which included some stereotypes, abnormal movements and postures, some respiratory disturbances, rats became quiet and sluggish in movements and there were periods of immobility. The observed hypo-locomotion was quantitatively verified by using two different types of activity cages. The fraction caused a significant decrease in the locomotor activity in both cages, the decrease was more remarkable in the activity wheel cage. The results suggested that C.c.cerastes venom has neurotoxic activity which is mainly concentrated in fraction 1. Both the crude venom and the purified fraction act primarily postsynaptically to depress muscle contractility.