The aim of the current study was to examine the effect of proportion and digestibility of grass-clover silage on dry matter intake (DMI), milk yield and nitrogen (N) excretion in lactating dairy cows. In total, 36 Danish Holstein dairy cows, 12 primiparous and 24 multiparous, were included in the study. At the beginning of the experiment the cows were on average (mean ± SD) 122 ± 81 days in milk (DIM). The cows were divided into 9 groups (4 cows in each group) based on parity and DIM, and were randomly assigned to one of four dietary treatments in a 4 x 4 Latin square design with 9 replications. The four dietary treatments differed in forage source as follows: 1) low proportion of low digestible grass-clover silage; 2) low proportion of high digestible grass-clover silage; 3) high proportion of low digestible grass-clover silage; 4) high proportion of high digestible grass-clover silage. Different proportions were obtained by exchanging grass-clover silage with maize silage (30:70 or 70:30 on DM basis). Different digestibilities of grass-clover silages were obtained by using two grass-clover silages differing in harvest time, spring growth and first re-growth, with these expected to have a high and low digestibility, respectively. The experiment was divided into 4 periods, all lasting for 3 weeks of which the first 17 d were used as adaption and the last 4 d were used for sampling and recording. Feed and water intake as well as milk yield were recorded daily, and milk samples were collected for determination of milk composition. In addition, faeces and blood samples were collected for chemical analyses. Replacing grass-clover silage with maize silage increased DMI and milk protein but reduced milk fat, whereas increased digestibility of grass-clover silage decreased DMI but increased milk protein. Milk yields (kg and kg of energy-corrected milk (ECM)) were not affected by diet, probably due to the increase in DMI observed in cows offered low digestible grass-clover. Excretion of N in urine increased with high proportion and low digestibility of grass-clover silage, probably a result of the greater crude protein (CP) concentration in grass-clover silages than in maize silage, and in low compared to high digestible grass-clover silage, respectively. Thus, proportion and digestibility of grass-clover silage surprisingly seemed to have only minor effect on milk production and composition. However, digestibility was confounded with the harvest used, and the different cuts of grass-clover silage likely differed in clover proportion, which could have affected the results. Finally, urinary N excretion increased with increased dietary CP concentration.