Rumen microbial protein synthesis (MPS) represents up to 75% of the nitrogen reaching the duodenum. However, the effect of increasing MPS on milk production has not been numerically assessed. The aim of this meta-analysis was to assess the relationship between rumen MPS and milk production of lactating dairy cows. A database was built from 35 publications (47 experiments) reporting rumen MPS and milk production measured on the same groups of animals. The primary objective of these experiments was to test the impact of nutritional strategies (carbohydrate, nitrogen, plant extracts, enzymes, forage) on MPS. When available, diet composition, intake, rumen fermentation parameters, total-tract nutrient digestibility and milk composition were also registered. Milk production and MPS averaged 28.5 kg/d (10.8 to 44.1 kg/d) and 1.70 kg/d (0.39 to 2.94 kg/d), respectively. For both parameters, the within-experiment variation was calculated: experiments presenting the 25% lowest variations were considered as having no variation in the targeted variable, and were excluded from further analyses. In total, 35 experiments reported a variation in MPS between treatments (>90 g/d) among which 28 also reported a variation in milk production (>0.75 kg/d). Changing carbohydrate source was the nutritional strategy with the highest probability (75%) of increasing MPS and milk production. To quantity the effect of a variation in MPS on milk production, a linear regression model was tested with MPS and experiment as fixed effects. One experiment was excluded to ensure normality of MPS and milk production. A significant relationship was shown (P < 0.001): milk production (kg/d) = 25.5 + 4.21 × MPS (kg/d), with 30 publications (34 experiments, 96 cows in total), residual standard error = 0.94 and adjusted R² = 0.98. Therefore, in the conditions of our meta-design, a 10% rise in MPS would increase milk production by 0.72 kg/d. Further work is required to determine the potential factors interfering this relationship.