Over the past two decades, research into the effects of essential oils (EOs) on rumen microorganisms as an alternative to antibiotics has intensified. Yet, there are few investigations on rumen protozoa. To evaluate if EOs have antiprotozoal efficacy against rumen protozoa, the present investigation was conducted. Using the potentiality of rumen protozoa to digest ¹⁴C-labeled bacteria, the influence of EOs on in vitro protozoal activity was determined. For the study, orange peel, cinnamon, laurel, oleaster, garlic, and thyme essential oils were selected. Control (without essential oil), 500 mg/kg, 1000 mg/kg, and 5000 mg/kg dosages were used. Except for garlic oil, all essential oils showed a notable effect on antiprotozoal activity. The highest antiprotozoal impact was reported at 500 mg/kg and 1000 mg/kg doses of thyme oil, with respective reductions of 89.1% and 84.8% in bacteria degraded by protozoa. Cinnamon and oleaster oils had the strongest antiprotozoal efficacy at a concentration of 5000 mg/kg. At 5000 mg/kg doses of oleaster and cinnamon oils, the quantity of ¹⁴C-labeled bacteria degraded by protozoa was reduced by 96% compared to the group that served as the control. In conclusion, orange peel, cinnamon, laurel, oleaster, and thyme oils demonstrated remarkable in vitro antiprotozoal activity; however, more comprehensive research is required to analyse the effects of the EOs used in this study on rumen living groups such as protozoa, bacteria, and yeast and on rumen dynamics.