The purpose of the current study was to determine if supplementing a Met derivative, N-acetyl-l-Met (NALM; CJ CheilJedang, Seoul, South Korea) would affect lactational performance and economic returns of Holstein dairy cows during early to mid-lactation. Sixty multiparous Holstein dairy cows in early lactation (27 ± 4.3 d-in-milk) were tested for 24 wk in a randomized complete block design. Animals were grouped based on actual milk yield and calving date. Dietary treatments included; 1) control (no NALM); 2) 15 g/d NALM (15NALM); 3) 30 g/d NALM (30NALM); and 4) 45 g/d NALM (45NALM). Diets were formulated to meet or exceed nutritional requirements of dairy cows producing at least 42 kg/d of milk and to insufficiently supply metabolizable Met (control). Data were analyzed using the MIXED procedure of SAS. Milk and its component prices used to calculate income-over feed cost (IOFC) were averaged for the entire trial. The IOFC for milk yield was calculated using the weighted average mailbox milk prices per hundredweight for reporting areas of all federal milk market. Feed prices were reflective of local prices. The IOFC was calculated based on the income generated from milk, and milk component yield relative to feed costs associated with actual dry matter intake. Intake of dry matter was similar across treatments, but numerically greater milk yield responses with 15NALM and 30NALM led to quadratic effects on feed efficiencies (P < 0.07). Likewise, the IOFC for milk yield was greatest with 30NALM (quadratic effect; P = 0.05), while it tended to be greater with NALM supplemented groups (P = 0.10) when compared with control. Quadratic trend was also observed for the IOFC based on milk component yield, as it was improved with 15NALM and 30NALM but tended to decrease with 45NALM compared with control (P = 0.08). Overall data in the present study imply that supplementing NALM at 30 g/d improved feed efficiencies, and these improvements contributed to sizable increases in IOFC based on milk (22.2%) and milk component (11.9%) yields. Therefore, NALM supplementation can be an option to improve economic returns of dairy farming.