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Our research project mainly focused on four Moroccan medicinal plants: Euphorbia resinifera, Equisetum ramosissimum, Eryngium atlanticum, and Daphne gnidium. Our aim was to study their effects on the bacterium Rhodococcus equi. In order to determine which plant had the greatest antimicrobial effect, tests were conducted using extracts from the decoction of these plants. Antibacterial activity was evaluated using the diffusion method in solid and liquid mediums. The antibacterial tests showed that only Euphorbia resinifera effectively inhibited the growth of Rhodococcus equi. The Equisetum ramosissimum, Eryngium atlanticum, and Daphne gnidium extracts had no effect on this bacterium. Next, we tested the extract from the decoction of Euphorbia resinifera on Rhodococcus equi in parallel with six antibiotics. The extract from the decoction of Euphorbia resinifera was a strong Rhodococcus equi growth inhibitor, according to the Mautrait and Raoult scale, because it induced a 25 mm inhibition halo. This value is comparable to that induced by chloramphenicol (CHL), which is the most effective antibiotic against this bacterium. CHL presented a 27.66 mm inhibition halo. However, the zones of inhibition were lower for amoxicillin (AMX), cephalothin (KF), and ampicillin (AMP), which had a 13 mm, 7 mm, and 5 mm diameter, respectively. Kanamycin (KMN) had no effect on this bacterium. These results show that the six antibiotics reacted differently to Rhodococcus equi, which appears to be sensitive to CHL and doxycycline (DOX). The extract from the decoction of Euphorbia resinifera exhibited the most significant antibacterial effect on the growth of Rhodococcus equi, with a MIC100 of 0.987 mg/ml. These results highlight the potential of this Moroccan endemic species as a source of compounds that modify antibiotic resistance. The use of such natural substances could represent a potential alternative against the etiologic agent of tuberculosis, Mycobacterium tuberculosis, which is a serious health issue in Morocco and Africa due to its similarities with Rhodococcus equi.