The objective of this study was to investigate the effect of feeding calcium salt of soybean oil at transition period of Holstein dairy cows. Twenty four multiparous Holstein dairy cows (700 ± 50 kg and 260 days in pregnant), were used in a completely randomized design. Treatment were: 1) control (cows that were not fed fat before and after calving); 2) cows were fed fat just after calving; 3) cows were fed just before calving, and 4) cows were on fat before and after calving. Cows in their respective treatments were received supplemental fat at 2, 1.2, 2.2% of DM at close up, first 21 DIM, and between 21-60 DIM, respectively. Also, productive performance and immune function of cows were investigated at these periods. At all periods, diets were isocaloric and isonitrogenic. Cows were fed as TMR ad-libitum at two equal portions in the morning and evening meals. Furthermore, dry matter intake, body weight changes, milk production and milk composition, and feed efficiency were studied. Using two times (on 30 and 40 DIM) SRBC (10%) shot the immune function of cows were investigated. Ten days after each stimulation date, blood samples were taken of jugular vein of stimulated cows to measure the antibody titer. Also, white blood cells, lymphocytes, neutrophils, and monocytes counts were measured. To study plasma lipid fractions, blood samples were taken on the days -14, -7, 0, 7, 14, 21, 28, 35, 42, 49, and 56 relative to calving. All data were analyzed using the mixed model procedure of SAS (SAS 9.1). Cow was the specified term for the random effect and covariance structure was modeled using an auto regressive structure. Feeding the calcium salt of soybean oil reduced dry matter intake before and after calving, but it was not changed in cows on fourth treatment. Cows on the third treatment had the highest milk production among treatments (P 0.0001). It may be attributed to the greater DMI in cows on it (P 0.05). Milk composition was similar among treatments and did not affect by treatments. Feed efficiency improved in cows fed supplemental fat (P 0.01). Before calving, there was no difference in plasma concentrations of triglycerides, VLDL, LDL, HDL and cholesterol among treatments but after calving plasma concentrations of triglycerides and LDL-cholesterol in second treatment was the highest among treatments (P 0.07 and. P 0.09 mmol.l -1 , respectively). There was no difference among treatments after first SRBC injection but was highest in cows fed fourth treatment after second injection (P 0.08). No difference was observed in white blood cells, lymphocytes, neutrophils, and monocytes counts among treatments, whereas cows fed the second treatment had the highest eosinophil count relative to other treatments (P 0.05). Results of current experiment indicated that feeding fat after calving can improve productive performance but not immune function. Also, cows