The objective of this study was to assess the effect of feeding rumen-protected methionine (RPM) pre- and postpartum on milk yield (MY) and composition up to 14 wk of lactation. Three weeks before calving, multiparous Holstein cows (n = 211) were randomly assigned to a control (CON) or RPM group, whereby the only difference in the diets was the inclusion rate of Smartamine M pre- (PreP) and postpartum (PostP). Methionine feeding (MP Met as % of MP) in the diet were 2.76 vs 3.35 PreP, and 2.10 vs 2.68 PostP, for CON and RPM, respectively. Diets were formulated using CNCPS v7 at DMI of 12.7 and 24.4 kg of DM/cow/d PreP and PostP, respectively. Diets were isoenergetic, and provided the same lysine supply (9.73 PreP and 7.10% of MP PostP, respectively), with a Lys:Met ratio of 3.5 vs 2.9 for CON and RPM PreP, and 3.4 vs 2.7 for CON and RPM PostP. Cows were allocated to pens (1 pen per group PreP, and 6 pens of 16 cows per group PostP), and the diets were fed to pens. Milk samples were collected at wk 1 and 2, and then biweekly until 14 weeks PostP. Data were analyzed by ANOVA with repeated measurements using PROC MIXED of SAS, with treatment (trt), pen(trt), week and trt by week as fixed effects and cow(pen trt) as a random effect. Supplementing RPM PreP and PostP increased milk true protein percentage from wk 2 to 14 (2.9 vs. 3.0%; P < 0.01), milk fat percentage from wk 8 to 14 (3.5 vs. 3.7%; P < 0.01), total solids percentage from wk 6 to 14 (12.2 vs. 12.5%; P < 0.01), milk urea nitrogen for all 14 weeks (8.42 vs. 8.82 mg/dl; P < 0.01), and tended to increase true protein yield (1.44 vs. 1.48 kg/d; P = 0.09). Feeding RPM tended to reduce milk lactose percentage (4.84 vs. 4.80%; P = 0.07). No effect was observed on MY (48.5 vs. 47.9 kg/d; P = 0.61), energy corrected milk (ECM, 49.9 vs. 50.5 kg/d; P = 0.31), milk fat yield (1.85 vs. 1.90 kg/d; P = 0.12), milk lactose yield (2.37 vs. 2.33 kg/d; P = 0.30), and total solids yield (6.14 vs. 6.17 kg/d; P = 0.61) for CON and RPM, respectively. Supplementing RPM pre- and postpartum improved lactation performance by increasing true protein percentage and yield, fat percentage, and total solids percentage, but did not affect total MY or ECM.