AbstractThe purpose of this study was to examine the effects of rumen‐protected methionine (RPM) supplementation on the reproductive and productive performance of primiparous dairy cows fed two levels of protein. The Presynch‐Ovsynch protocol was used to synchronize 36 lactating Holstein cows that were assigned randomly to one of six dietary treatments: (1) 14% CP and without RPM diet (14CP‐0RPM; n = 6), (2) 14% CP and 15 g/head/day RPM (14CP‐15RPM; n = 6), (3) 14% CP and 25 g/head/day RPM (14CP‐25RPM; n = 6), (4) 16% CP and without RPM diet (16CP‐0RPM; n = 6), (5) 16% CP and 15 g/head/day RPM (16CP‐15RPM; n = 6), and (6) 16% CP and 25 g/head/day RPM (16CP‐25RPM; n = 6). Independent of CP levels, feeding RPM had reduced the calving interval (P < 0.01). Feeding RPM increased (P < 0.01) overall plasma progesterone (P4). Feeding 16CP‐15RPM increased (P < 0.01) overall plasma P4. Feeding 16% CP increased (P < 0.01) 4% fat corrected milk, energy corrected milk, milk fat and protein yield, and milk casein. Moreover, feeding the 25RPM has increased (P < 0.01) 4% fat corrected milk, energy corrected milk, milk fat, and protein yield. Compared with other treatments, feeding 16CP‐25RPM or 16CP‐15RPM enhanced (P < 0.01) milk yield and milk fat yield. In conclusion, feeding 16% CP with RPM boosted the productivity and reduced the calving interval in primiparous lactating dairy cows.