The aim of the study was to compare the influence of fat supplementation in the form of full-fat soybean seeds and hydrolyzed palm oil as energy sources for dairy cows in early lactation.During the first 8 lactation weeks, 17 dairy cows divided into group S (n = 8) and group C (n = 9) were observed. The basic diet was the same for both groups. The differences were in the composition of the concentrate mixture, which had a balanced content of nutrients. In group S the fat source was heat-treated soybean seeds, while in group C the fat source used was hydrolyzed palm oil. The two diets started to be fed on the day of calving. Blood samples were taken weekly (1 st -5 th week) and 8 weeks after delivery. At the end of the experiment ruminal fluid was taken. During the experiment BCS in both groups deteriorated similarly. In group S it decreased from 3.8 ± 0.2 to 3.3 ± 0.3 and in group C from 3.5 ± 0.4 to 3.1 ± 0.4. A better performance of hepatic metabolism was proved in group S. In group S lower concentrations of non-esterified fatty acids were identified in the 3 rd (0.96 ± 0.38 vs. 1.76 ± 0.63 mmol·l ; p < 0.05) week after calving. The gamma-glutamyl transferase (EC 2.3.2.2) activity in serum indicates a better liver parenchyma condition in group S where no increased activity was identified above the reference range. An increased activity was identified in group C from the 2 nd week with a significant difference between groups detected in the 2 nd (0.41 ± 0.07 vs. 0.66 ± 0.25 µkat·l -1 ; p < 0.05) and 4 th (0.42 ± 0.05 vs. 0.64 ± 0.25 µkat·l -1 ; p < 0.05) weeks after delivery. There were no significant differences found between groups in bilirubin and aspartate transaminase (EC 2.6.1.1) but a general tendency toward lower values is apparent in group S. No significant differences were found between groups by the examination of ruminal fluid.Based on these results we can conclude that full-fat soy was better utilised than hydrolysed palm oil and represents a suitable alternative for increasing energy concentration in the diet for dairy cows. On the other hand, the development of liver steatosis in cows make controversial the usage of fat as an energy source for fresh cows even if their BCS is around 3.5-3.8 and it may not be recommended generally. Soy, liver, lipid mobilization, blood, BCS, isoenzymes LDHLack of energy is the main limiting factor to high yields of dairy cows. Taking into account the low intake of dry matter and the fast increase of milk production in dairy cows after calving, it is important to provide a high energy concentration in the diet during this period. One possibility of solving the energy deficit in dairy cows in this period is to use supplementary fats. The main reason for using fat is its 2-3 times higher energy content compared to saccharides or proteins. The source of fat for dairy cows should have a high content of pure energy, high digestibility, acceptable palatability and price and should be easily manipulated. Fat in the diet can come from different sources, such as natu...