This study was conducted at North Carolina State University, USA. Primiparous (n=9) and multiparous (n=17) Holstein cows were utilized in a completely randomized block design. Three treatments were as follows : (1) control treatment ( CON) without fat supplementation ; (2) unprotected fat treatment (UF), which fat supplemented as soybean oil; (3) protected fat (PF), which fat supplemented as Megalac . Fats were supplemented to the cows diets beginning at 21 days prior to expect calving date through 60 days postpartum. Supplemental fats were fed at 2% and 3% dietary dry matter (DM) during prepartum and postpartum periods, respectively. Milk production measured daily. Milk fat, protein, lactose and solids not fat (SNF) were analyzed at day 0, 30 and 60 postpartum. The results indicated that, prepartum dry matter intake (DMI) was not significantly different across treatments. However, fat supplementation decreased postpartum DMI compared to the CON treatment. Cows fed PF beginning in the prepartum period produced more milk and higher FCM than cows fed UF and CON treatments. Feeding PF numerically increased milk fat percentage compared to the CON and UF diets, but the difference was not significant among treatments. However, PF treatment tended to decreased (P=0.10) milk protein percentage compared to CON and UF treatments. Feeding fat did not alter milk lactose and solids not fat percentages in comparison with CON diet. Feed efficiency, expressed as kg of 3.5% FCM per kg of DM intake, was significantly higher when feeding fat treatments than feeding CON. Concentration of C8:0 in milk fat tended to be higher (P=0.10) in cows fed fat compared to CON treatment. Fat supplementation had no significant effect on production of C12:0 , C14:0 , C15:0 , C18:1 and C18:2 in milk fat . However, significant differences were found in C10:0, C16:0 and C18:0 in UF and PF treatments compared to CON treatment. From the present results it can be concluded that supplementation of protected fat in the rations of high producing dairy cows during prepartum and postpartum led to positive effect on milk production and milk composition.