Knowledge on the flux of nitrogen (N) excreted through urines is essential in animal nutrition since it may provide information on animal N metabolism and the extent of environmental N pollution. Both the 15N natural enrichment of animal proteins over the diet (Δ15Nanimal-diet) and the milk urea N (MUN) concentration have been previously linked to N partitioning. The objective of this meta-analysis was to test the effect of combination of Δ15Nanimal-diet in plasma and MUN for predicting the urinary N excretion (UNE) in dairy cows. Individual data on Δ15Nanimal-diet in plasma, MUN, and UNE of 177 cow/period observations were evaluated by meta-analysis. Data were analyzed by mixed-model regression analysis. When model was fitted with either Δ15Nanimal-diet or MUN, both biomarkers were capable to independently predict UNE. However, when Δ15Nanimal-diet and MUN were combined in one model, both biomarkers remained significant and the error of the model decreased. In conclusion, both Δ15Nanimal-diet and MUN can predict UNE and their combination can strengthen the prediction capacity of the model.