Arginine-vasopressin (AVP) can take not only its essential hormonal effects, but can also provide various extrahormonal influence. AVP acts not only as a neuropeptide in the adult brain but may play a significant role during maturation of the central nervous system. The half-life of AVP-molecule average 10 – 15 minutes. To increase its bioavailability the AVP structural analogue Acetyl-D-Methionine-Proline-Arginine-Glycine-Amide (Ac-D-Met-Pro-Arg-Gly-NH₂) was synthesized. Previous researches have shown that both AVP and its analogue administration provide modulatory effects on white rats behavioral skills formation. The presented research is aimed to reveal postponed effects of Ac-D-Met-Pro-Arg-Gly-NH₂ neonatal administration. Peptide was administered intranasally in the dose of 10 ng/kg on days 8 to 14 following the day of birth. Control animals received distilled water. The behavioral reactions of mature animals (63–70 days) were studied in next tests: "active avoidance task " and "intricate food maze". In the "active avoidance task " test the increase of number of correct trials on the 2th and on the 4th days of learning and during the control of the skill conservation was revealed. In the "intricate food maze" test the increase of the same parameter on the 2nd day of learning, the decrease of exit from the first maze compartment latency during all period of learning and the decrease of reaction time on the 4th day of learning were displayed. Data obtained allow to affirm, that neonatal administration of Ac-D-Met-Pro-Arg-Gly-NH₂ lead in mature rats to the improvement of learning with both negative and positive reinforcement. The possible explanation is that the time of peptide administration is all-important to vasopressinergic system formation.