Our objective in current study was to investigate the effects of feeding fat supplements rich in linoleic acid ( ca-salt of soybean oil ) on immune response of Holstein dairy cows in transition period and their calves’ performance, immune response, and blood parameters. Twenty four multiparous Holstein dairy cows (700 ± 50 kg and 260 days in pregnant; n = 12 for each treatment), were used in a completely randomized design. Treatment were: 1) Control group (calves that their dams did not receive fat supplements), and 2) Fat group (calves that their dams received fat supplements at 2% of dietary DM. Diets were balanced according to NRC 2001 and were isocaloric and isonitrogenous. Since 41 d before anticipated calving date, and in order to minimize the difference among cows and equilibrate their body condition scores, cows were housed in an individual stalls and fed with farm routine ration. Then 21 d before anticipated calving date, cows were fed dietary treatments as TMR and ad-libitum at two equal portions in the morning and evening meals. Upon calving, cows were milked and colostrums sampled. After calving, calves were housed in individual stalls and received their dam’s colostrums at the rate of 10% of body weight for 3 consecutive days. Calves had free access to water and starter and received an equal amount of whole milk throughout the experiment. Calves performance and immune response were studied. Blood sampling were done on the day of birth, 1, 3, 10, and 21. In order to stimulate calves immune system 1.5 cc SRBC (10%) shot (on the day of 38 and 48) was injected and ten day after each shot blood sampled. Data were analyzed using the MIXED procedure of SAS (SAS Institute, 2003). Calf was the specified term for the repeated measures, whereas the best covariance structure was compound symmetry based on the smallest Bayesian criterion. Differences between treatments were declared significant at P ? 0.05 and means were compared using the Tukey multiple comparison test. Feeding fat did not affect cow’s final weight and body weight changes at prepartum period, although dry matter intake of cows fed control diet was greater than those of fat group. Blood plasma parameters of cows including triglyceride, cholesterol, very low and high density lipoproteins were not affected by treatments. Results showed that feeding ca-salt of soybean oil did not affect colostrums volume and their respective constituents. Also, birth weight was not differed among treatments but calves in fat group had greater dry matter intake. Average daily gain but not feed efficiency was greater in calves in fat group compared to calves in control group. Calves in fat group were weaned ten day earlier than that of control group. Amount of blood anti-body at first and second stimuli and also blood white cells count including lymphocytes, neutrophils, eosinophils and monocytes were not affected by treatments.