We determined the relationship between amino acid (Met and Lys) and fat supplementation on the yield of milk and milk components of mid- to late-lactation dairy cows. Thirty-six Holstein cows (154 ± 52 DIM) were used in a truncated Latin square with a 2x2 factorial arrangement of treatments with 2 consecutive 35 d periods, with the final 5 d used for sample and data collection. Treatment diets were: 1) Control diet containing no supplemental fat or amino acids (diet contained 86 and 89% of predicted Met and Lys requirements, respectively; CON); 2) Diet containing supplemental fat (1.5% diet DM; 83% C16:0-enriched supplement) and no amino acid supplementation (FA); 3) Diet containing amino acid supplementation (105 and 98% of predicted Met and Lys requirements, respectively) and no supplemental fat (AA); 4) Diet containing supplemental fat and supplemental amino acids (FA+AA). The statistical model included the random effect of cow and fixed effects of supplemental fat, supplemental amino acids, period, and their interactions. There was no effect of treatment on body weight, body condition score change, protein yield, or energy-corrected milk. No interactions between amino acid and fat supplementation were observed for DMI and yields of milk and milk components. Overall, compared with CON, amino acid supplemented diets decreased milk yield (43.6 vs 45.1 kg/d, P < 0.01) and increased DMI (31.9 vs 31.3 kg/d, P < 0.01), milk fat content (3.68% vs 3.52%, P < 0.01), and milk protein content (3.25% vs 3.17%, P < 0.01). Compared with CON, fatty acid supplemented diets increased milk fat content (3.66% vs 3.52%, P < 0.01) and milk fat yield (1.60 vs 1.56 kg/d, P = 0.03). Compared with CON, fatty acid supplemented diets tended to increase 3.5% fat-corrected milk (45.2 vs 44.8, P = 0.09). Both amino acid and fatty acid supplemented diets tended to increase body condition score compared with CON (3.42 vs 3.38, P = 0.09; and 3.42 vs 3.38, P = 0.06, respectively). In conclusion, amino acid supplementation to mid- to late-lactation cows increased milk fat and protein content but did not increase yields. Fatty acid supplementation increased milk fat content and yield and tended to increase 3.5% fat-corrected milk yield.