The objective of this study was to evaluate the effects of increasing doses of a lysine derivative N-acetyl-l-Lys (NALL, CJ CheilJedang, Seoul, South Korea), on the performance of lactating dairy cows fed corn silage-based diets. Sixteen multiparous lactating Holstein dairy cows (parity = 2 to 3; 60–70 d-in-milk) were used in a 4 × 4 Latin square design with 21-d experimental periods. Diets were formulated using NDS Professional (R.U.M.&N, Reggio Emilia, Italy), a software based on the Cornell Net Carbohydrate and Protein System equations (CNCPS v.6.5) to supply adequate metabolizable energy but inadequate metabolizable Lys (−7 g/d) for dairy cows producing 42 kg/d of milk with 3.8% milk fat, and 3.2% milk protein. Cows were blocked by DIM and assigned to one of 4 treatments: 1) 0 g/d NALL (control); 2) 40 g/d NALL (40NALL); 3) 80 g/d NALL (80NALL); and 4) 120 g/d NALL (120NALL). The fixed effects of treatment and period and random effects of cows nested within square were tested using the GLIMMIX procedure of SAS. Intake of dry matter linearly increased (P = 0.04) with increasing NALL supplementation and was for 80NALL (24.3 kg/d). Milk yield increased (P = 0.02) with 80NALL and 120NALL (45.6 kg/d) compared with the control and 40NALL (43.2 kg/d). Milk fat yield was unaffected, whereas milk protein yield linearly increased (P = 0.05) with increasing NALL supplementation. Milk lactose yield tended to increase linearly (P = 0.07) with increasing NALL supplementation. Concentration of MUN was the greatest with 120NALL (quadratic trend; P = 0.02). In contrast, there were no effects of NALL supplementation on concentrations of blood glucose, BHB, total ruminal VFA concentration, ammonia N or molar proportion of VFA. Nonesterified fatty acid concentration tended to be lower (P = 0.08) for 40NALL and 80NALL. Concentrations of plasma Lys were similar across all treatments (P = 0.15). In conclusion, NALL supplemented at 80 g/d improved feed intake and milk yield but not ruminal fermentation.