This study analyzed the consequence of malnutrition and/or serotoninergic manipulation during the period of fast growth of encephalon on the somatic development in rats. It was used the protocol of measurement of indicators of this development proposed by Silva et al., 2005. The protocol was applied from 1st to 21st day and rats were breastfed by female which received control diet (commercial diet, Labina) with 23% of protein, normoproteic diet, nourished animals (Group Nourished Nour), n=15 or were breastfed by female which after the delivery received hypoproteic diet (Regional Basic Diet RBD), with 8% of protein, malnourished animals (Group Malnourished Maln) n=15. It were observed in the group malnourished a decrease of corporal weight from 4th day, of latero-lateral axis of skull from 8th to 21st day, of antero-posterior axis of skull from 10th to 21st day, of longitudinal axis and length of tail from 7th to 21st day of life (p 0,05) The study emphasized the hypothesis that malnutrition in critical period of development, interferes on somatic development of rats. Besides that, it was emphasized that the use of protocols with definition of anatomic points and suitable choice of material and accuracy of measurements provide a higher uniformity in periods which were observed the deleterious effects in all studied axes