The present study aimed to estimate digestible protein (DP) requirements for maintenance and growth and assess the efficiency of protein utilization in pacu (Piaractus mesopotamicus) juveniles. A complete randomized design consisted of seven treatments, and five replicates (tanks) per treatment was used. After a one-week acclimation period, 350 pacu juveniles of 27.48 ± 1.8 g (initial average body weight - BW) were equally distributed among 35 tanks (10 fish per tank) of 450 L. Fish were fed with seven graded digestible protein levels (64.5, 111.8, 164.6, 217.1, 264.4, 316.2 and 369.5 g kg-1) three times a day until apparent satiation for 120 days. The monomolecular model parameters including nitrogen maintenance requirement (NMR) (37.76 mg BW0.67 kg-1 d-1), daily nitrogen deposition (ND) (194.8 mg BW0.67 kg-1 d-1), and protein intakes (based on metabolic BW) of 1638, 1902, and 2241 mg kg-1BW0.67 d-1 for 75, 80 and 85% maximum theoretical nitrogen retention (NRmaxT), respectively and the efficiency of protein utilization (529×10-6) were estimated through the relationship between nitrogen intake (NI) and ND. The digestible protein requirements for 75, 80, and 85% of NRmaxT were estimated as 187, 217, and 256 g kg-1 respectively by the monomolecular model based on the daily feed intake of 2% of live BW of pacu juveniles.