Abstract: The present study was conducted to discuss the effects of Dunaliella salina powder（DSP）on milk performance and immune function.18 healthy Holstein cows in mid lactation were randomly blocked into three groups（control group,1.5 times of vitamin A group and DSP group）.The results showed that the addition of DSP or 1.5 times of vitamin A in the diet of dairy cows could improve the milk performance and that DSP group was better than 1.5 times of vitamin A group.The milk somatic cell counts were significantly decreased for the DSP group,and the concentration of IgG and IgM in serum also showed a significantly increasing tendency.The addition of 1.5 times of vitamin A could significantly decrease the milk somatic cell counts,and the serum IgG content also tended to increase.