Abstract: This experiment was conducted to study the effect of replacing alfalfa (Medicago sativa) hay with alfalfa silage on milk production and quality, forage digestibility, blood biochemical indices and economic benefits in dairy cows. Fifteen healthy multiparous Chinese Holstein cows with similar body weight, milk yield and parity at mid lactation were randomly allocated to 3 groups, with 5 cows in each group. The control group fed a total mixed ration diet of 4.0 kg alfalfa hay/(head·d). The trial groups A and B were fed 4.4 kg and 8.8 kg alfalfa silage, equivalent to 2.0 kg and 4.0 kg of alfalfa hay on a dry matter basis, respectively. The trial lasted 64 days. There were no differences between the control group and test groups in dry matter intake (P>0.05). Milk yield in the control group was significantly higher than that in B group (P<0.05), but was not different to A group (P>0.05). Protein, fat and lactose content in the milk were improved in the test groups with the increased silage substitution, but only the milk fat content in B group was significantly higher than that in control group (P<0.05). The apparent digestibility of NDF and Ca in the test groups did not different from the control (P>0.05). The apparent digestibility of crude protein and phosphorus did not different between A and B groups (P>0.05). In contrast, the test groups had a significantly lower apparent crude protein digestibility and significantly higher phosphorus digestibility than the control group (P<0.05). There were no differences among the test groups and control group for cow blood total protein, albumin, urea nitrogen, glucose and carbon dioxide (P>0.05). Compared with the control group, the economic benefit of group A was 0.61 yuan/(head·d). This research showed that substituting 4.4 kg alfalfa silage for 2.0 kg alfalfa hay can improve the production performance, milk quality and economic benefits.