It is well known that ACTH/MSH-like peptides affect CNS development, learning process and exploratory behavior. Analogue of ACTH(4-10) fragment Semax (MEHFPGP) was shown to exert marked neurotropic and neuroprotective activities, but devoid of a hormonal one. It was shown that Semax administration during 1-3 weeks of postnatal development result in decrease of anxiety and depression and has positive influence on learning capacity of white rats. It was demonstrated earlier that stressful treatment during early postnatal period causes notable changes in physiology and behavior in future. The aim of present study is to determine the long-lasting effects of neonatal stress and estimation of possibility to correct neonatal stress consequences by Semax administration. Stress was elicited by daily maternal deprivation from postnatal day (PND) 2 to until PND 15 for 5 hours. Control animals were not subjected to maternal deprivation. Semax was daily intranasally injected from PND15 until PND 29 in the dose 0.05 mg/kg. The animals of control group received equivalent volume of vehicle in the same period. Postnatal testing: 3 groups of rats were used in this work – nonstressed control rats; stressed control rats; stressed rats, received Semax. Animal's behavior was studied during second month of life. Exploratoty activity, anxiety and locomotor activity were evaluated in open field (OF) test and elevated plus maze (EPM) test. Rat's learning capacity was estimated in complex maze with food reinforcement. The rats exposed to stress demonstrated increased anxiety level and hyperactivity in OF test and EPM test. Learning capacity of stressed animals was significantly decreased. Semax administration attenuated neonatal stress negative effects. The work was supported by the Program of Basic Research "Molecular and Cell Biology", Program Scientific School ([numero] 5638.2006.4) and Russian Fond of Basic Reseach ([numero] 07-04-00733).