New-born rats are known to undergo important brain metabolic changes during first 4-5 weeks of their lives. However precise description of metabolic changes at latter stages is missing. At this period rats might still undergo changes due to final brain maturation what may impact data interpretation of experiments during this window. This study aimed to explore possible metabolic changes in the rat brain during the late post-natal period (post-natal days 29 - 77), using in-vivo 1H and 31P-MRS and a temporal resolution of 1 week. We report significant changes in Ins, tCho (mainly due to GPC increase), Tau and Glu in rats considered as young adults.