Abstract: Yarrow (Achillea millefolium) means thousands leaves plant and belongs to Asteraceae family. Yarrow is a gramineous perennial plant which grows in mountainous regions of Europe, North Africa and East Asia (including North Iran and Alborz heights). This plant has many health benefits like treating problems of digestive system, respiratory system, cardiovascular system (stimulating blood circulation and lowering blood pressure) and genital-urinary system. In this study, the effect of Yarrow extract was evaluated on immunity parameters of blood serum in little female laboratory rats (Balb/C race). At first, samples were divided randomly in 5 groups: three treatment groups, one control group and one placebo group. Each group had eight members and all groups were kept in similar conditions. Hydroalcoholic extract was prepared in three doses including 50, 100 and 200 mg kg^-1 and was injected in peritoneum every 2 days for 20 days. Normal saline was injected to placebo group. All measurements were done using Protein Electrophoresis Method. Measured parameters were albumin amount, α-1 and α-2 globulin, β globulin, gamma globulin, albumin globulin ratio and total protein. Results showed that the amount of albumin, β globulin and total protein were increased in all three doses. A-2 were decreased in all treatments and α-1 were increased in all three doses but this increase was significant for doses 100 and 200 mg. Albumin globulin ratio was increased also in all treatments but it was significant only for 50 mg. Gamma globulin amount was increased in 50 and 100 mg but decreased a little in 200 mg. Results of this study showed that Yarrow extract caused significant changes in blood immune parameters and can affect immune system of body even in absence of antigenic factors.