Abstract The purpose of the three trials reported here was to measure the efficiency of lysine utilization for growth and lysine requirement for maintenance of Nile tilapia (Oreochromis niloticus) during three growing stages. For the initial phase, a total of eight treatments (4.04, 6.63, 9.80, 13.3, 16.6, 20.7, 25.6 g lysine kg−1 and an additional diet containing 6.79 g lysine kg−1 called counter-proof) were randomly distributed among 36 experimental units, each containing 15 fishes of 2.35 ± 0.05 g. The grower and finisher phase consisted of seven treatments (4.13, 7.99, 11.7, 15.3, 19.4, 22.9 g lysine kg−1 and an additional diet containing 7.75 g lysine kg−1) randomly distributed among 21 experimental units of eleven (433 ± 12.49 g) and nine (733 ± 11.24 g) fishes, respectively. The counter-proof treatment confirmed that lysine was the first-limiting amino acid in all three growing stages. Overall, growth performance, feed efficiency and fillet yield were improved with lysine intake. In the grower and finisher phase, Nile tilapia fed diet containing the lower level of lysine exhibited reduction in protein weight and increase in body lipid content, indicating that the reminiscent energy, once used to deposit protein in fish consuming sufficient amount of lysine, was used for lipid deposition. The efficiency of lysine utilization of 0.60, 0.60 and 0.59 during the initial, grower and finisher phase, respectively, equating to approximately 115 mg lysine/g protein, proved to be the same (P > 0.05) and independent of the growth stage. The requirement for maintenance was estimated as 22.7, 45.1, and 56.3 mg lysine/kg0.8 body weight in the initial, grower and finisher phase, respectively, suggesting that maintenance requirements change with age or size (P