To determine the effects of diets supplemented with protected fat (PF) on milk production and reproductive performance, fifteen lactating Holstein cows weighing 490-540 Kg and having 1-4 parities were divided in a completely randomized block design into three similar groups. Cows in the 1^st group were individually fed the control diet, while those in the 2^nd and 3^rd groups were fed control diet supplemented with 3% and 5% of Ca salt of fatty acids (Magnapac) on dry matter basis of concentrate feed mixture (CFM), respectively. The experimental feeding period lasted from 2-3 weeks pre-partum up to the 120 day-post-partum or conception. At calving, duration of placental drop (PD) and uterine involution (UI) were determined. Live body weight (LBW), body condition score (BCS), feed intake (FI) and average daily milk yield (ADMY) were biweekly recorded at the 15 , 30, 45 and 60 lactation days. During the post-partum period, interval from calving to conception (DO), and then number of services per conception (NSC) were recorded. Results showed insignificant differences in LBW, however, cows in 5% PF group showed slight increase in LBW (1.4%) versus reduction in LBW of 3% PF (-2.9%) and control (-5.1%) groups. There were insignificant group differences in BCS, although BCS of 5% PF group was the best as compared to 3% PF or control groups.FI fro CFM of 5% PF group was lower than those of 3% and control groups (10.59 vs. 10.99 and 11.15 kg), but the difference was not significant. ADMY was higher (P<0.05) in 5% than in 3% and control groups (25.19 vs. 24.33 and 24.25 kg/60 d lactation). The duration of PD markedly reduced (P<0.05) by about 3.6 and 3.1 days and UI reduced (P≥0.05) by 3.2 and 3.0 days in 3 and 5% PF groups as compared to the control group, respectively. Also, NSC reduced (P<0.05) to 1.6 and 1.2 services in 3 and 5% PF groups as compared to 3 services in control group. Number of DO was shorter (P<0.05) in 3 and 5% PF groups (40.2 and 46.2 d) than in control one (88.6 d). Feeding PF diets at a level of 5% increased milk yield, feed efficiency and reproductive performance, but showed economic feed efficiency lower than feeding lactating Holstein cows on the control diet.