Rumen-protected methionine (RPM) could be an important tool to optimize nutrition and health in transition dairy cows. Therefore, the objective of this study was to investigate the effects of RPM during early lactation on productive and metabolic parameters of dairy cows. The trial was conducted in a commercial herd in Paraná State, Southern Brazil, from January to February 2017. A total of 42 cows were blocked by lactation order and calving date. The treatment group received 12 g daily of methionine (Smartamine^®, Adisseo) and 38 g of corn meal, while the control group received 50 g/cow/d of corn meal. The supplementation was carried out for 29 ± 8 d postpartum, beginning at calving. Total mixed ration (TMR) samples were collected weekly throughout the experiment period. Six blood samples were collected on d 0, 1, 3, 5, 7, and 14 postpartum. Data were analyzed using the MIXED procedure of SAS with a model containing the effects of calving order, treatment, time, and treatment*time interaction as fixed effects and cow within treatment as a random effect. Milk yield in the first 30 d of lactation did not differ (34.9 kg/d in the control and 33.6 kg/d in the RPM group; SEM = 1.6 kg/d, P = 0.53) between experimental groups. Animals supplemented with RPM produced milk with higher fat content (4.07 vs. 3.59% ± 0.11; P < 0.01) and higher fat to protein ratio (1.14 vs. 1.05 ± 0.03; P < 0.05) than control cows. There was a trend of the methionine supplemented cows to produce milk with higher protein (3.58 vs. 3.45% ± 0.05; P = 0.07) and casein (2.82 vs. 2.72% ± 0.05; P = 0.10) contents and higher milk energy output (26.7 vs. 24.4 Mcal/d ± 1.1; P = 0.13) than control cows. Analysis of metabolites on serum blood (NEFA, BHB, bilirubin, Ca, albumin, glucose, total protein, cholesterol, triglycerides, urea, and aspartate aminotransferase) and urine (creatinine, urea, and uric acid) did not demonstrate (P > 0.10) any beneficial effects of RPM, possibly as a result of supplementation only in the postpartum period. In summary, methionine supplementation in the immediate postpartum period showed positive results restricted to milk composition.