The cytoplasmic serine/threonine ribosomal protein S6 kinase (S6K1) plays a critical role in controlling protein translation. There is evidence that amino acids regulate S6K1 and protein synthesis in avian species, but the effect of dietary protein level on the activation of S6K1 in neonatal chicks is unknown. Therefore, the aim of the present experiment was to investigate the effect of different protein levels, supplied during the first 5d post-hatch, on body growth, breast muscle development and on the activation of S6K1 and its downstream target. the S6, in neonatal chicks. Chicks were fed a pre-starter diet during the first 5d post-hatch containing low (19.6% crude protein (CP); LP), medium (23.1 % CP: MP) or high (26.7 % CP) levels (HP) of protein. Weight gain of chicks fed the HP diet was higher (P<0.05) compared with (hose fed the LP diet during day (d)3-d5 and the numerical advantage of this group was maintained from d2 to d7. On d2 and d3, greater levels of S6K1 and S6 phosphorylation and/or activity were observed in chicks receiving the HP diet compared with LP and MP diets, without differences between results of the latter two dietary treatments. In conclusion. the present results Suggest that early protein nutrition impacts the development of broiler chicks.