The objective of the study was to determine the influence of the herbal preparation Ruchamax®, added to rations for heifers on the number of ciliates in their rumen, ruminal fermentation, and some biochemical parameters in their blood serum. The experiment was carried out on three rumen-fistulated heifers. The control diet (K), comprising 84% of meadow hay and 16% of concentrate, and two experimental diets, composed of the control ration, supplemented with Ruchamax®, were supplied in doses. The experimental groups were fed a diet with 20 g of Ruchamax® administered once a day for 5 (R5) or 14 days (R14). After 5 or 14 days of administration, samples of rumen fluid and blood were taken. In rumen fluid, the number of protozoa, pH, and the concentrations of VFA and ammonia nitrogen, were determined, whereas total protein, urea, total cholesterol, ASP, ALT, and ALP, were measured in blood serum. Supplementation with Ruchamax® significantly increased the number of total ciliates and the genus Entodinium in group R14 compared with the control animals and group R5. The number of ciliates from the genus Ophryoscolex decreased in the rumen of group R14 compared with R5. The number of protozoa from the family Isotrichidae significantly decreased in group R14 compared with the control heifers. The administration of Ruchamax® for 5 days increased the concentrations of ammonia nitrogen and total VFA, but decreased pH in the rumen. In group R14, the molar proportion of propionate, the sum of isoacids, and valerate increased, but acetate decreased significantly compared to the control heifers. Urea and total cholesterol level in serum blood increased after 14 days of supplementation with Ruchamax®. The activities of AST and ALT significantly decreased in group R5 compared with the control animals.