Metabolizable protein (MP)-deficient diets have been shown to reduce N excretion of dairy cows. However, such diets may limit synthesis of milk and milk protein possibly due to deficiencies in EAA, particularly Met, Lys, and His (MLH), insufficient energy supply or both. We aimed to investigate the interactions between rumen-protected (RP) MLH and starch level on performance of dairy cows fed MP-deficient diets. Sixteen multiparous Holstein cows (138 ± 46 DIM, 46 ± 6 kg/d milk) were used in a replicated 4 × 4 Latin square with 2 × 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for sample collection. Treatments included high-starch (HS), HS + RPMLH, reduced starch (RS), and RS + RPMLH. The basal diets consisted (DM basis) of 35.7% corn silage, 14.7% haylage, and 49.6% concentrate. Dietary energy level varied by replacing 30% ground corn with 20% beet pulp and 10% soyhulls. Dietary NE_L, starch, and CP averaged 1.68 Mcal/kg, 34.4% and 16.0% for HS diets, and 1.59 Mcal/kg, 12.3% and 16.4% for RS diets, respectively. Smartamine M, Aji-Pro L, and an Ajinomoto prototype His product were supplemented to meet digestible MLH requirements. Data were analyzed with the MIXED procedure of SAS. Compared with RS diets, feeding HS diets increased yields of milk (37.9 vs. 40.1 kg/d) and milk true protein (1.07 vs. 1.16 kg/d) and decreased DMI (25.4 vs. 24.7 kg/d). Feed and milk N efficiency were greater in cows fed HS vs. RS diets. Concentration of milk true protein increased, while that of milk fat decreased with HS vs. RS diets. Both MUN and PUN were lowered for HS vs. RS diets. Supplementation of RPMLH improved milk true protein concentration. Starch level by RPMLH interactions were observed for plasma Arg and Lys, with elevated values in cows fed RS diets. Increased dietary energy reduced the plasma concentrations of all EAA except Met and Thr. Plasma Met and His were increased by RPMLH. In conclusion, enhanced dietary energy by replacing fibrous byproducts with ground corn improved yields of milk and milk protein through better use of dietary N and elevated mammary uptake of EAA.