This experiment was conducted to study the safety supplemental dosage of Eucommia ulmoides leaf extract for lactating dairy cows. Sixty Chinese Holstein cows were randomly allocated to 4 groups with 15 replicates per group and 1 cow per replicate based on the same weight, parity, duration of lactation and milk yield. The control group was fed with the basal diet, and the experimental groups were fed with the basal diet supplemented with 20, 100 and 200 g/(d·cow) Eucommia ulmoides leaf extract, respectively. The adaptation period to the diet was 10 days while the formal experimental period was 60 days. The results showed as follows: adding appropriate Eucommia ulmoides leaf extract [20 g/(d·cow) could increase dry matter intake, milk yield and milk fat percentage of lactating dairy cows, and decrease somatic cell count (SCC); the dry matter intake in 100 g/(d·cow) Eucommia ulmoides leaf extract group could be reduced by 0.78% compared with that in control group (P>0.05), and the milk yield decreased by 1.38% compared with that in control group (P>0.05); the dry matter intake in 200 g/(d·cow) Eucommia ulmoides leaf extract group could be significantly reduced by 3.42% compared with that in control group (P<0.05), and the SCC in 200 g/(d·cow) Eucommia ulmoides leaf extract group was significantly increased compared with that in the other three groups (P<0.05). Adding appropriate Eucommia ulmoides leaf extract [20 g/(d·cow) could increase dry matter intake, milk yield and milk fat percentage of lactating dairy cows, and decrease somatic cell count (SCC); the dry matter intake in 100 g/(d·cow) Eucommia ulmoides leaf extract group could be reduced by 0.78% compared with that in control group (P>0.05), and the milk yield decreased by 1.38% compared with that in control group (P>0.05); the dry matter intake in 200 g/(d·cow) Eucommia ulmoides leaf extract group could be significantly reduced by 3.42% compared with that in control group (P<0.05), and the SCC in 200 g/(d·cow) Eucommia ulmoides leaf extract group was significantly increased compared with that in the other three groups (P<0.05). Adding appropriate Eucommia ulmoides leaf extract [20 g/(d·cow)] could promote nutrient digestibility of lactating dairy cows, but adding high-dose Eucommia ulmoides leaf extract [200 g/(d·cow)] could cause the inhibition of nutrition digestion of lactating dairy cows. Adding high-dose Eucommia ulmoides leaf extract [100 and 200 g/(d·cow)] hadn't a negative effect on blood indices of lactating dairy cows. It is concluded that 100 g/(d·cow) Eucommia ulmoides leaf extract is advised as the highest dose of security based on production practice.